Enable autotest client package fetching based on updated image.

server/site_autotest.py

 import os
-from autotest_lib.server import installable_object
+from autotest_lib.client.common_lib import global_config
+from autotest_lib.server import autoserv_parser, installable_object
+
+
+config = global_config.global_config
+parser = autoserv_parser.autoserv_parser
+
 
 class SiteAutotest(installable_object.InstallableObject):
 
     def get(self, location = None):
         if not location:
             location = os.path.join(self.serverdir, '../client')
             location = os.path.abspath(location)
         installable_object.InstallableObject.get(self, location)
         self.got = True
 
 
+    def get_fetch_location(self):
+        if not parser.options.image:
+            return super(SiteAutotest, self).get_fetch_location()
+
+        repos = config.get_config_value('PACKAGES', 'fetch_location', type=list,
+                                        default=[])
+        new_repos = []
+        for repo in repos[::-1]:
+            if repo.endswith('static/archive'):
+                path = parser.options.image.rstrip('/')
+                build = '/'.join(path.split('/')[-2:])
+                repo += '/%s/autotest' % build
+            new_repos.append(repo)
+        return new_repos
+
+
 class _SiteRun(object):
     pass