Display upstream sha when git out of sync (#238)

We currently still have a somewhat opaque error when you're local and remote repo is out-of-sync.  Showing the expected sha should help a bit.

cmd/plural/deploy.go

@@ -99,14 +99,14 @@ func (p *Plural) build(c *cli.Context) error {
 	if err := CheckGitCrypt(c); err != nil {
 		return errors.ErrorWrap(errNoGit, "Failed to scan your repo for secrets to encrypt them")
 	}
-	changed, err := git.HasUpstreamChanges()
+	changed, sha, err := git.HasUpstreamChanges()
 	if err != nil {
 		return errors.ErrorWrap(errNoGit, "Failed to get git information")
 	}
 
 	force := c.Bool("force")
 	if !changed && !force {
-		return errors.ErrorWrap(errRemoteDiff, "Local Changes out of Sync")
+		return errors.ErrorWrap(errRemoteDiff, fmt.Sprintf("Expecting HEAD at commit=%s", sha))
 	}
 
 	if c.IsSet("only") {

pkg/utils/git/repo.go

@@ -36,20 +36,20 @@ func CurrentBranch() (b string, err error) {
 	return
 }
 
-func HasUpstreamChanges() (bool, error) {
+func HasUpstreamChanges() (bool, string, error) {
 	repo, err := Repo()
 	if err != nil {
-		return false, err
+		return false, "", err
 	}
 
 	ref, err := repo.Head()
 	if err != nil {
-		return false, err
+		return false, "", err
 	}
 
 	res, err := GitRaw("ls-remote", "origin", "-h", fmt.Sprintf("refs/heads/%s", ref.Name().Short()))
 	if err != nil {
-		return false, err
+		return false, "", err
 	}
 
 	scanner := bufio.NewScanner(strings.NewReader(res))
@@ -62,7 +62,7 @@ func HasUpstreamChanges() (bool, error) {
 		}
 	}
 
-	return remote == ref.Hash().String(), nil
+	return remote == ref.Hash().String(), remote, nil
 }
 
 func Init() (string, error) {