Set uploader to current user in "patchset-created" event upon cherry-picking

When using the web ui (both old and new ChangeScreen) to cherry-pick a
change to a branch that already has this change (e.g.: cherry-picking
on the same branch to get rid of dependencies), the corresponding
patchset-created event had its patchSet.uploader set to the Change's
owner instead of the current user. We now set it to the current user,
so stream-events consumers can properly detect who uploaded the
rebased patch set.

Bug: 60781
Change-Id: I0613ecae06b7843b8ca0294f83378c3917c26810
Upgrade sshd to include the fix for hash mismatch

It seems the fix for SSHD-330:
  https://issues.apache.org/jira/browse/SSHD-330
might will fix the hash mismatch error of bug 53895.

Hence, we upgrade gerrit to use a custom build of the SSHD library,
which is upstreams 0.9.0 (7d10ee49efa70dbacc8be788a2724b4f56a81ff0),
with

  28a8ae258b08c6b41ab64ac25f2331168dc0415a (SSHD-254 Suppress
  'Authentication with partial success' message on standard
  authentication)

(see gerrit's e5b7f1aa5c195098cdd043a21aa2734dd0764db4), and a
backport of

  2aed686bdb21681a421033c6ee5997e5cd8a9a83 ([SSHD-330] Handshake fails
  (wrong shared secret) 1 out of 256 times)

.

Bug: 53895
Change-Id: I2b12522b5a84ba8a3b97d4f577d0b33151b96b5e