mr create: Set default target branch

The default branch on gitlab projects can be changed from master to other
values.  The 'mr create' command defaults to 'master' and should use the
project's default branch instead.

Use the project's default branch instead of 'master'.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>

cmd/mr_create.go

@@ -26,7 +26,7 @@ var mrCreateCmd = &cobra.Command{
 	Use:     "create [remote [branch]]",
 	Aliases: []string{"new"},
 	Short:   "Open a merge request on GitLab",
-	Long:    `Creates a merge request (MR created on origin master by default)`,
+	Long:    `Creates a merge request (default: MR created on default branch of origin)`,
 	Args:    cobra.MaximumNArgs(2),
 	Run:     runMRCreate,
 }
@@ -124,14 +124,15 @@ func runMRCreate(cmd *cobra.Command, args []string) {
 	if err != nil {
 		log.Fatal(err)
 	}
-	targetBranch := "master"
+
+	targetBranch := targetProject.DefaultBranch
 	if len(args) > 1 && targetBranch != args[1] {
 		targetBranch = args[1]
 		if _, err := lab.GetCommit(targetProject.ID, targetBranch); err != nil {
 			err = errors.Wrapf(
 				err,
-				"aborting MR, target branch %s not present on remote %s. did you forget to push?",
-				targetBranch, targetRemote)
+				"aborting MR, %s:%s is not a valid target. Did you forget to push %s to %s?",
+				targetRemote, branch, branch, targetRemote)
 			log.Fatal(err)
 		}
 	}