libtest: allow committing to alternative branches

This will be used by the upcoming test-admin-upgrade-endoflife.sh

Closes: #874
Approved by: cgwalters

tests/libtest.sh

@@ -446,6 +446,7 @@ os_repository_new_commit ()
 {
     boot_checksum_iteration=${1:-0}
     content_iteration=${2:-0}
+    branch=${3:-testos/buildmaster/x86_64-runtime}
     echo "BOOT ITERATION: $boot_checksum_iteration"
     cd ${test_tmpdir}/osdata
     rm boot/*
@@ -464,7 +465,7 @@ os_repository_new_commit ()
 
     version=$(date "+%Y%m%d.${content_iteration}")
 
-    ${CMD_PREFIX} ostree --repo=${test_tmpdir}/testos-repo commit  --add-metadata-string "version=${version}" -b testos/buildmaster/x86_64-runtime -s "Build"
+    ${CMD_PREFIX} ostree --repo=${test_tmpdir}/testos-repo commit  --add-metadata-string "version=${version}" -b $branch -s "Build"
     cd ${test_tmpdir}
 }