tablet.py refactoring phase 1

Added a start_vtocc function. It works, but there's still
a lot of duplicate code.
queryservice_test revamp test_env getting better
queryservice_test: merged TestEnv classes into one
Better error reporting in split, adding at least tablet name everywhere.
Using the same connection to lock and unlock tables
for multisnapshot. That way it will work better.
queryservice_test: final touches
Merge branch 'rowcache'
Merge branch 'master' into parser