Adding more data in topology serving graph.

Also making vtctld parallelized for serving graph retrieval,
and also only querying the serving graph, not global topology.
Adding display of source tablet to vttablet binlog status.

Also properly handling thread safety within a single binlog player.
Small tweak from review.
VTTablet: Test case for Consolidator
queryservice: fix race in RowcacheInvalidator

There was a race condition between Stop, which would set
evs to nil before run could return, which caused run to
crash-loop.
Instead of Close setting evs to nil, we just wait for run
to exit, and run already sets evs to nil.
Merge branch 'rowcache'