[LibGit2] Teach tests to be resilient to init.defaultBranch

If a user runs the tests with a `~/.gitconfig` that provides an
`init.defaultBranch` that is not `master`, our tests fail.  Let's adjust
to the user's configuration as appropriate.

stdlib/LibGit2/test/libgit2.jl

@@ -634,7 +634,7 @@ mktempdir() do dir
     commit_oid1 = LibGit2.GitHash()
     commit_oid2 = LibGit2.GitHash()
     commit_oid3 = LibGit2.GitHash()
-    master_branch = "master"
+    master_branch = LibGit2.getconfig("init.defaultBranch", "master")
     test_branch = "test_branch"
     test_branch2 = "test_branch_two"
     tag1 = "tag1"
@@ -958,15 +958,15 @@ mktempdir() do dir
                     # various branch properties
                     @test LibGit2.isbranch(brref)
                     @test !LibGit2.isremote(brref)
-                    @test LibGit2.name(brref) == "refs/heads/master"
+                    @test LibGit2.name(brref) == "refs/heads/$(master_branch)"
                     @test LibGit2.shortname(brref) == master_branch
                     @test LibGit2.ishead(brref)
                     @test LibGit2.upstream(brref) === nothing
 
                     # showing the GitReference to this branch
                     show_strs = split(sprint(show, brref), "\n")
                     @test show_strs[1] == "GitReference:"
-                    @test show_strs[2] == "Branch with name refs/heads/master"
+                    @test show_strs[2] == "Branch with name refs/heads/$(master_branch)"
                     @test show_strs[3] == "Branch is HEAD."
                     @test repo.ptr == LibGit2.repository(brref).ptr
                     @test brnch == master_branch
@@ -1050,7 +1050,7 @@ mktempdir() do dir
                 @test tag2 in tags
 
                 refs = LibGit2.ref_list(repo)
-                @test refs == ["refs/heads/master", "refs/heads/test_branch", "refs/tags/tag1", "refs/tags/tag2"]
+                @test refs == ["refs/heads/$(master_branch)", "refs/heads/test_branch", "refs/tags/tag1", "refs/tags/tag2"]
                 # test deleting a tag
                 LibGit2.tag_delete(repo, tag1)
                 tags = LibGit2.tag_list(repo)
@@ -1334,7 +1334,7 @@ mktempdir() do dir
             add_and_commit_file(repo, "file1", "111\n")
             # switch back, add a commit, try to merge
             # from branch/merge_a
-            LibGit2.branch!(repo, "master")
+            LibGit2.branch!(repo, master_branch)
 
             # test for showing a Reference to a non-HEAD branch
             brref = LibGit2.GitReference(repo, "refs/heads/branch/merge_a")
@@ -1347,7 +1347,7 @@ mktempdir() do dir
 
             add_and_commit_file(repo, "file2", "222\n")
             upst_ann = LibGit2.GitAnnotated(repo, "branch/merge_a")
-            head_ann = LibGit2.GitAnnotated(repo, "master")
+            head_ann = LibGit2.GitAnnotated(repo, master_branch)
 
             # (fail to) merge them because we can't fastforward
             @test_logs (:warn,"Cannot perform fast-forward merge") !LibGit2.merge!(repo, [upst_ann], true)
@@ -1360,7 +1360,7 @@ mktempdir() do dir
             mv(joinpath(LibGit2.path(repo),"file1"),joinpath(LibGit2.path(repo),"mvfile1"))
             LibGit2.add!(repo, "mvfile1")
             LibGit2.commit(repo, "move file1")
-            LibGit2.branch!(repo, "master")
+            LibGit2.branch!(repo, master_branch)
             upst_ann = LibGit2.GitAnnotated(repo, "branch/merge_b")
             rename_flag = Cint(0)
             rename_flag = LibGit2.toggle(rename_flag, Cint(0)) # turns on the find renames opt
@@ -1445,7 +1445,7 @@ mktempdir() do dir
             LibGit2.branch!(repo, master_branch)
 
             fetch_heads = LibGit2.fetchheads(repo)
-            @test fetch_heads[1].name == "refs/heads/master"
+            @test fetch_heads[1].name == "refs/heads/$(master_branch)"
             @test fetch_heads[1].ismerge == true # we just merged master
             @test fetch_heads[2].name == "refs/heads/test_branch"
             @test fetch_heads[2].ismerge == false
@@ -1683,7 +1683,7 @@ mktempdir() do dir
             # add yet another file
             add_and_commit_file(repo, "file4", "444\n")
             # rebase with onto
-            newhead = LibGit2.rebase!(repo, "branch/a", "master")
+            newhead = LibGit2.rebase!(repo, "branch/a", master_branch)
 
             newerhead = LibGit2.head_oid(repo)
             @test newerhead == newhead
@@ -1693,7 +1693,7 @@ mktempdir() do dir
             pre_abort_head = add_and_commit_file(repo, "file6", "666\n")
             # Rebase type
             head_ann = LibGit2.GitAnnotated(repo, "branch/a")
-            upst_ann = LibGit2.GitAnnotated(repo, "master")
+            upst_ann = LibGit2.GitAnnotated(repo, master_branch)
             rb = LibGit2.GitRebase(repo, head_ann, upst_ann)
             @test_throws BoundsError rb[3]
             @test_throws BoundsError rb[0]
@@ -1718,7 +1718,7 @@ mktempdir() do dir
 
             a_head = LibGit2.head_oid(repo)
             add_and_commit_file(repo, "merge_file1", "111\n")
-            LibGit2.branch!(repo, "master")
+            LibGit2.branch!(repo, master_branch)
             a_head_ann = LibGit2.GitAnnotated(repo, "branch/merge_a")
             # merge returns true if successful
             @test_logs (:info,"Review and commit merged changes") LibGit2.merge!(repo, [a_head_ann])