SERVER-10448 change default explain mode from queryPlanner to executionStats
SERVER-14444 Don't call stepDown in ReplicationCoordinatorImpl (yet)
SERVER-1424 (re)smoke tag parsing and new test library, v0

Includes:
- Smoke.py options for filtering by jstest tags
- New resmoke.py test utility in v0 alpha
- Lots of example resmoke configurations
- SCons integration for unittests
- Sample tagged jstests
SERVER-15248 Convert QuorumChecker into a ScatterGatherAlgorithm.
SERVER-15248 Use a ScatterGatherAlgorithm in ElectCmdRunner.
SERVER-15248 Convert FreshnessChecker to use a ScatterGatherAlgorithm.

Also, use completion functions instead of scheduling work on events to handle
election phase transitions in repl_coordinator_impl_elect.cpp.  Leads to less
scheduling, and easier-to-follow code.
Revert "SERVER-1424 (re)smoke tag parsing and new test library, v0"

This reverts commit fac5571f67e23a1339e20e0621bab0ba2a6b7163.
Merge remote-tracking branch 'upstream/master'