update_layer.py: move the location of transaction.atomic()

It doesn't need to be so ahead since we only need it when writing database, and
a following patch will remove layerbranch from database when the branch had
been removed from the repo, it's not easy to do the work in
transaction.atomic() block.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>

layerindex/update_layer.py

@@ -238,8 +238,6 @@ def main():
     # why won't they just fix that?!)
     tinfoil.config_data.setVar('LICENSE', '')
 
-    try:
-        with transaction.atomic():
     layer = utils.get_layer(options.layer)
     urldir = layer.get_fetch_dir()
     repodir = os.path.join(fetchdir, urldir)
@@ -268,6 +266,8 @@ def main():
             logger.info("Skipping update of layer %s - branch %s doesn't exist" % (layer.name, branchdesc))
         sys.exit(1)
 
+    try:
+        with transaction.atomic():
             newbranch = False
             if not layerbranch:
                 # LayerBranch doesn't exist for this branch, create it