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
queryz: fix wrapping and add Reason to output
Merge branch 'suguwork'
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
misc bug fixes

- Remove spammy warning message from event streamer.
- Fix panic on double-close of memcache connection.
- Disallow non-identifier table names even if it's back-quoted.
query service: load schema safety

Add some safety around how we load schema by back-quoting table
names. This will prevent unexpected crashes if a badly-named
table makes it through.
Merge branch 'suguwork'