Backport of tablet3 changes and its tests.
Added integration test to Makefile.
Renamed tablet3.py and vt_occ2.py, misc other fixes.
Merge remote-tracking branch 'origin/master' into tablet3
Do not allow uncoditional tablet updates.
Merge branch 'master' into no-minus-1
Merge remote-tracking branch 'origin/master' into tablet3
Merge branch 'master' into resharding