Allow user to specify git path for mirror manifest.

In some case, especially local_manifest.xml for mirror, user may want to
specify a different gitdir path.

Change-Id: Ib0a639e9014811701fbc4eccc3b03330d9b9f4b2
Signed-off-by: Scott Fan <fancp2007@gmail.com>

manifest_xml.py

diff --git a/manifest_xml.py b/manifest_xml.py
index 53f3353..7725317 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -711,7 +711,7 @@
     relpath = path
     if self.IsMirror:
       worktree = None
-      gitdir = os.path.join(self.topdir, '%s.git' % name)
+      gitdir = os.path.join(self.topdir, '%s.git' % path)
     else:
       worktree = os.path.join(self.topdir, path).replace('\\', '/')
       gitdir = os.path.join(self.repodir, 'projects', '%s.git' % path)