Add -t to branch-stx.sh to enable a tag-only mode

We need to be able to tag final releases without creating a new branch.
Changing the starting branch (formerly 'master') to be the same as the
destination branch has the desired effect so the -t option does that
in addition to skipping the automatic .gitreview update.

Note that setting the source branch (SRC_BRANCH) to something other than
master is also something we will need in the regualt branching mode
now that we have default (working) branches in some of the staging
repos set to names similar to stx/v1.2.3 to represent the starting point
in the upstream repo of our working branch.

Change-Id: Id0cb485a4f8a2ebd3feaf602a140f66ed3b91322
Signed-off-by: Dean Troyer <dtroyer@gmail.com>

release/branch-stx.sh

@@ -11,6 +11,8 @@
 # -m <manifest>     Extract the repo list from <manifest> for starlingx
 #                   and stx-staging remotes
 #
+# -t                Set tag only (sets SRC_BRANCH == BRANCH)
+#
 # <repo-url>        Specify one or more direct repo URLs to branch (ie git remote)
 #                   These are appended to the list of repos extracted from the
 #                   manifest if one is specified.
@@ -29,6 +31,10 @@
 # BRANCH is the actual branch name, derived by adding 'm/' (for milestones) or
 # 'r/' (for periodic releases) to SERIES.
 #
+# SRC_BRANCH is the starting point for the new branch.  Needed when the working
+# branch is not named 'master'.  When SRC_BRANCH == BRANCH this is effectively
+# a tag-only operation.
+#
 # TAG is the release tag that represents the actual release, derived by adding
 # a 'patch' version to SERIES, initially '0'. If TAG is unset no tag is created.
 #
@@ -47,7 +53,7 @@ set -e
 # Defaults
 MANIFEST=""
 
-optspec="lm:n-:"
+optspec="lm:nt-:"
 while getopts "$optspec" o; do
     case "${o}" in
         # Hack in longopt support
@@ -73,6 +79,9 @@ while getopts "$optspec" o; do
         n)
             DRY_RUN=1
             ;;
+        t)
+            TAG_ONLY=1
+            ;;
     esac
 done
 shift $((OPTIND-1))
@@ -96,6 +105,14 @@ TAG=${TAG:-$SERIES.0}
 # The list of remotes to extract from MANIFEST
 REMOTES="starlingx stx-staging"
 
+if [[ -n $TAG_ONLY ]]; then
+    # Force source and target branches to be the same
+    SRC_BRANCH=${BRANCH}
+fi
+
+# The starting branch
+SRC_BRANCH=${SRC_BRANCH:-master}
+
 # This is where other scripts live that we need
 script_dir=$(realpath $(dirname $0))
 
@@ -136,7 +153,8 @@ function branch_repo {
     fi
 
     pushd $repo_dir >/dev/null
-    git checkout master
+    git checkout $SRC_BRANCH
+    git pull origin $SRC_BRANCH
 
     if ! git branch | grep $BRANCH; then
         # create branch
@@ -162,7 +180,10 @@ function branch_repo {
             echo "### skipping push to $branch"
         fi
 
+        if [[ -z $TAG_ONLY ]]; then
+            # Skip .gitreview changes for tag-only mode
             update_gitreview $branch
+        fi
     else
         # Do the Github way
         # push