build: set osusergo build tag by default

This PR activates the osuergo build tag in GNUMakefile. This forces the os/user
package to be compiled without CGO. Doing so seems to resolve a race condition
in getpwnam_r that causes alloc creation to hang or panic on `user.Lookup("nobody")`.

GNUmakefile

@@ -21,7 +21,7 @@ ifndef BIN
 BIN := $(GOPATH)/bin
 endif
 
-GO_TAGS ?=
+GO_TAGS ?= osusergo
 
 ifeq ($(CI),true)
 GO_TAGS := codegen_generated $(GO_TAGS)