repo download: add --cherry-pick option

default option uses git checkout, and thus overwrite the previous
checkouts.  this is a problem for automated builds of several
changesets in the same project for daily builds of pending submission

You can now use:
repo download [--cherry-pick|-c] project changeid/patchnumber

This will parse the manifest, cd to the corresponding project
download the changes to FETCH_HEAD and cherry-pick the result.

This is useful to automate cherry-picking of a patch
in the context of build automation, and commit gating (e.g. buildbot)

Change-Id: Ib638afd87677f1be197afb7b0f73c70fb98909fe
Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>

project.py

@@ -1637,6 +1637,14 @@ class Project(object):
       if self._allrefs:
         raise GitError('%s checkout %s ' % (self.name, rev))
 
+  def _CherryPick(self, rev, quiet=False):
+    cmd = ['cherry-pick']
+    cmd.append(rev)
+    cmd.append('--')
+    if GitCommand(self, cmd).Wait() != 0:
+      if self._allrefs:
+        raise GitError('%s cherry-pick %s ' % (self.name, rev))
+
   def _ResetHard(self, rev, quiet=True):
     cmd = ['reset', '--hard']
     if quiet:

subcmds/download.py

@@ -33,7 +33,9 @@ makes it available in your project's local working directory.
 """
 
   def _Options(self, p):
-    pass
+    p.add_option('-c','--cherry-pick',
+                 dest='cherrypick', action='store_true',
+                 help="cherry-pick instead of checkout")
 
   def _ParseChangeIds(self, args):
     if not args:
@@ -78,4 +80,7 @@ makes it available in your project's local working directory.
           % (project.name, change_id, ps_id, len(dl.commits))
         for c in dl.commits:
           print >>sys.stderr, '  %s' % (c)
-      project._Checkout(dl.commit)
+      if opt.cherrypick:
+        project._CherryPick(dl.commit)
+      else:
+        project._Checkout(dl.commit)