Print project name when work tree initialization fails

When syncing a lot of projects in parallel, it is not otherwise
clear which one of them has failed to init work tree.

Change-Id: I8edfb4955023389a499e99cfa511bdc0d2850ba2

project.py

@@ -2589,7 +2589,7 @@ class Project(object):
         cmd.append('-v')
         cmd.append(HEAD)
         if GitCommand(self, cmd).Wait() != 0:
-          raise GitError("cannot initialize work tree")
+          raise GitError("cannot initialize work tree for " + self.name)
 
         if submodules:
           self._SyncSubmodules(quiet=True)