forall: exit 1 if we skip any repos

If a repo doesn't exist (e.g. an incomplete sync), make sure we exit
non-zero when they get skipped.

Change-Id: Ifff711e374416b1e6b9b8da4fdc6f14b27ced450
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/239235
Reviewed-by: David Pursehouse <dpursehouse@collab.net>
Tested-by: Mike Frysinger <vapier@google.com>

subcmds/forall.py

@@ -323,10 +323,10 @@ def DoWork(project, mirror, opt, cmd, shell, cnt, config):
     cwd = project['worktree']
 
   if not os.path.exists(cwd):
-    if (opt.project_header and opt.verbose) \
-    or not opt.project_header:
+    if ((opt.project_header and opt.verbose)
+        or not opt.project_header):
       print('skipping %s/' % project['relpath'], file=sys.stderr)
-    return
+    return 1
 
   if opt.project_header:
     stdin = subprocess.PIPE