cherry-picked the bidirectional partition change from mongodb/mongo@0d6aff9

This will help us fix rollback_simple1.js (#374) and other replset tests.

Original commit message:
"""
SERVER-8558 Support mongobridge delay parameter in ReplSetBridge

This should be compatible with future improvements to support ranged delays (see #317)

Support unidirectional network partitioning in ReplSetTest
The default behavior (bidirectional) remains as-is. This adds support for terminating an X->Y link while leaving Y->X untouched.

Test replica set flapping and heartbeatTimeoutSecs

Also adds two fail points to support JS tests. rsDelayHeartbeatResponse will delay the replSetHeartbeat command response on a node. rsStopHeartbeatRequest may be used to preemptively fail a heartbeat to another member (by its host:port).

Signed-off-by: Eric Milkie <milkie@10gen.com>
"""
Merge branch 'bidirectional-partition'
refs #374, fix test to make sure original primary does not step down
Merge branch 'bugs/374b'
changed buildbot to have separate community and enterprise builders for concurrency
fixed force scheduler
removed enterprise parameter from force scheduler because it's implied by the builder now
added some debugging info to logpath.js to help resolve bb fails
fix logpath.js on buildbot machines #396
Merge branch 'logpath'

Conflicts:
	jstests/logpath.js
Merge remote-tracking branch 'origin/master' into putmultiple