Have fake_cipd accept 'export' in addition to 'ensure'.

Change-Id: Ia82e81a2d4b5fc37856e9abbda79681b61f6fcd0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4492323
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Josip Sokcevic <sokcevic@chromium.org>
Auto-Submit: Brian Ryner <bryner@google.com>

testing_support/fake_cipd.py

@@ -30,7 +30,7 @@ def parse_cipd(root, contents):
 
 
 def main():
-  assert sys.argv[1] == 'ensure'
+  assert sys.argv[1] in ['ensure', 'export']
   parser = argparse.ArgumentParser()
   parser.add_argument('-ensure-file')
   parser.add_argument('-root')