Fix thread lock around cachepath access.

git_cache.py

Index: git_cache.py
diff --git a/git_cache.py b/git_cache.py
index 1ac9a41c23f56aa147a0131eda6eb9cb574ef864..d6ed2a82d313980da46e1f0d5bd936fce043c0f5 100755
--- a/git_cache.py
+++ b/git_cache.py
@@ -200,7 +200,9 @@ class Mirror(object):
 
   @classmethod
   def SetCachePath(cls, cachepath):
+    cls.cachepath_lock.acquire()
     setattr(cls, 'cachepath', cachepath)
+    cls.cachepath_lock.release()
 
   @classmethod
   def GetCachePath(cls):
@@ -215,7 +217,7 @@ class Mirror(object):
         cls.cachepath_lock.release()
         raise RuntimeError('No global cache.cachepath git configuration found.')
       setattr(cls, 'cachepath', cachepath)
-      cls.cachepath_lock.release()
+    cls.cachepath_lock.release()
     return getattr(cls, 'cachepath')
 
   def RunGit(self, cmd, **kwargs):