deploy: Fixes for TestDeploy.

* Update MERGE_EVENTS.
* Make rootfs rw.

BUG=chromium:955057
TEST=betty-release-tryjob

Change-Id: I4d06f09461fe1eddb378170f0086ed602d0befd7
Reviewed-on: https://chromium-review.googlesource.com/1580380
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Achuith Bhandarkar <achuith@chromium.org>
Reviewed-by: Nicolas Norvez <norvez@chromium.org>
Reviewed-by: LaMont Jones <lamontjones@chromium.org>
diff --git a/cli/deploy_unittest.py b/cli/deploy_unittest.py
index b104102..b7f05bd 100644
--- a/cli/deploy_unittest.py
+++ b/cli/deploy_unittest.py
@@ -37,7 +37,7 @@
     self.port = None
     self.lsb_release = None
 
-  def IsDirWritable(self, _):
+  def MountRootfsReadWrite(self):
     return True