Buck: Strip SNAPSHOT suffix in artifact names only for GERRIT repositories

Maven artifact names on Google bucket replacing SNAPSHOT suffix with
timestamp. 731967591ef98ab3c94691ba9dc0f217630dda76 changed this by
preserving the SNAPSHOT suffix. This broke fetching of gwtorm and
gwtjsonrpc and was reverted by 731967591ef98ab3c94691ba9dc0f217630dda76.

This change fixes this for both worlds: stripping it for GERRIT and
GERRIT_API Maven repositories but preserving it for the rest.

Test plan:

maven_jar() is working as expected for the both worlds:

* gwtorm:gwtorm:1.10-SNAPSHOT-20140310.015132-1 (repo = GERRIT)
* org.eclipse.jgit:org.eclipse.jgit:3.4.0-SNAPSHOT (repo = MAVEN_LOCAL)

Change-Id: I5357abe9ad6a40538c444ad70016c8c6d75d8ff3
Update gwtorm to 1.7.1

Change-Id: Ia9ba26bdda20a053bc3a267c5c9efad37e76ab77
Expose Atlassian's maven repository

Change-Id: Ie6c8ff50f4ed6460aa7cbdea707d97fdd1f86a40
Update SSHD to 0.11.1-atlassian-1

Use custom build of SSHD library from Atlassian's maven repository,
that fixes sporadic handshake failures [1].

[1] https://issues.apache.org/jira/browse/SSHD-330

Change-Id: I4258f515ac10e04c8c8f1850f060b9dbad6d876f
Update 2.8.6 release notes with recent fixes

Change-Id: I58376c245026e3f940703c986bd8c5789cb9ed3b