Use email in tryjob ref name instead of username.

GoB doesn't have a concept of username so it can't restrict access only
to 'refs/tryjobs/${username}/*' like old Gerrit did.

GoB knows about user email though and at some point it will restrict
access to 'refs/tryjobs/${useremail}/*'.

TEST=ran 'cbuildbot --remote -p chromiumos/chromite --buildbot --debug amd64-generic-paladin' and verified try bot picked up my CL. 

Change-Id: I81588ef99cbb364a8a017bd5a38f658067e83fd1
Reviewed-on: https://chromium-review.googlesource.com/167480
Tested-by: Vadim Shtayura <vadimsh@chromium.org>
Reviewed-by: Chase Phillips <cmp@chromium.org>
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>
Reviewed-by: David James <davidjames@chromium.org>
diff --git a/buildbot/remote_try.py b/buildbot/remote_try.py
index e48b2b7..3e42973 100644
--- a/buildbot/remote_try.py
+++ b/buildbot/remote_try.py
@@ -136,7 +136,7 @@
     # TODO(rcui): convert to shallow clone when that's available.
     current_time = str(int(time.time()))
 
-    ref_base = os.path.join('refs/tryjobs', self.user, current_time)
+    ref_base = os.path.join('refs/tryjobs', self.user_email, current_time)
     for patch in self.local_patches:
       # Isolate the name; if it's a tag or a remote, let through.
       # Else if it's a branch, get the full branch name minus refs/heads.