Add --max-in-flight argument to vtgate.

This is a means to limit the amount of queueing which can occur, which
should cause failure states to report as such faster rather than
becoming sinks for queries.
Fixup unit test.
Add new client-side error type to represent request backlog errors.

fixup
Include innodb dir in bootstrap archive.

Leaving it out breaks MariaDB replication status tables.
Use pre-installed MariaDB instead of downloading it.
Merge pull request #78 from plobsing/vtgate-max-inflight

Vtgate max inflight
Merge branch 'suguwork'
query_service: added support for admin statements

Support for SHOW, DESCRIBE, EXPLAIN and ANALYZE.
query_service: official PLAN_SELECT_STREAM plan id
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
Add EnableSSL() to mysql.ConnectionParams.
Print start time when running integration tests.
Add connect_dict() to Tablet class to use DictCursor.