refactored binary build subshell invocation

Signed-off-by: Steve Kuznetsov <skuznets@redhat.com>

hack/common.sh

@@ -252,7 +252,17 @@ os::build::build_static_binaries() {
 #     then just the host architecture is built.
 os::build::build_binaries() {
   # Create a sub-shell so that we don't pollute the outer environment
-  (
+  ( os::build::internal::build_binaries "$@" )  
+}
+
+# Build binaries targets specified. Should always be run in a sub-shell so we don't leak GOBIN
+#
+# Input:
+#   $@ - targets and go flags.  If no targets are set then all binaries targets
+#     are built.
+#   OS_BUILD_PLATFORMS - Incoming variable of targets to build for.  If unset
+#     then just the host architecture is built.
+os::build::internal::build_binaries() {
     # Check for `go` binary and set ${GOPATH}.
     os::build::setup_env
 
@@ -319,7 +329,6 @@ os::build::build_binaries() {
           "$(dirname ${test})"
       done
     done
-  )
 }
 
 # Generates the set of target packages, binaries, and platforms to build for.