Improve translation jobs

Looking at [1], I see "Cannot rebase: You have unstaged changes.", let's
add a "git status" to see what might be the reason.

Looking at [2], an error occurs since releasenotes/source/locale is not
under version control. This can happen if the project has translated
files on a branch from copying. Ignore the failure.

[1]
http://logs.openstack.org/periodic/git.openstack.org/openstack/networking-bgpvpn/master/propose-translation-update/dda4792/job-output.txt.gz
[2]
http://logs.openstack.org/periodic/git.openstack.org/openstack/trove-dashboard/stable/pike/propose-translation-update/8deef07/job-output.txt.gz

Change-Id: Ia4f4863a60a64d5f6333e4550a548b8ed3fe56f5

jenkins/scripts/common_translation_update.sh

@@ -326,6 +326,8 @@ EOF
         # Don't submit if we have the same patch id of previously submitted
         # patchset
         if [[ "${PREV_PATCH_ID}" != "${CUR_PATCH_ID}" ]]; then
+            # Show current status of tree for debugging purpose
+            git status
             # Do error checking manually to ignore one class of failure.
             set +e
             # We cannot rely on the default branch in .gitreview being

jenkins/scripts/propose_translation_update.sh

@@ -234,7 +234,9 @@ function propose_releasenotes {
     # Remove any releasenotes translations from stable branches, they
     # are not needed there.
     if [[ "$version" != "master" && -d releasenotes/source/locale ]]; then
-        git rm -rf releasenotes/source/locale
+        # Note that content might exist, e.g. from downloaded translations,
+        # but are not under git control.
+        git rm --ignore-unmatch -rf releasenotes/source/locale
     fi
 }