update.py: check whether branch existed when nocheckout

Fixed:
Assume there is no master branch in hello layer:
$ update.py -l hello -b master
INFO: Skipping update of layer hello - branch master doesn't exist

This is correct since hello layer doesn't have master branch, but when --nocheckout:
$ update.py -l hello -b master  --nocheckout
[snip]
INFO: Sorting layers for branch mater:
WARNING: Cannot find required collections on branch master:
WARNING: hello: LAYERDEPENDS: <snip>

This is incorrect, this patch fixed the problem, now it skips it since the
branch doesn't exists when --nocheckout.

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

layerindex/update.py

@@ -345,10 +345,10 @@ def main():
                     repo = git.Repo(repodir)
                     assert repo.bare == False
                     try:
+                        # Always get origin/branchname, so it raises error when branch doesn't exist when nocheckout
+                        topcommit = repo.commit('origin/%s' % branchname)
                         if options.nocheckout:
                             topcommit = repo.commit('HEAD')
-                        else:
-                            topcommit = repo.commit('origin/%s' % branchname)
                     except:
                         if newbranch:
                             logger.info("Skipping update of layer %s - branch %s doesn't exist" % (layer.name, branchdesc))

layerindex/update_layer.py

@@ -362,10 +362,9 @@ def main():
     # Collect repo info
     repo = git.Repo(repodir)
     assert repo.bare == False
+    topcommit = repo.commit('origin/%s' % branchname)
     if options.nocheckout:
         topcommit = repo.commit('HEAD')
-    else:
-        topcommit = repo.commit('origin/%s' % branchname)
 
     tinfoil = None
     tempdir = None