comment even says so

if something goes wrong with this test

need to call lockMeta before we synchronize on the Database object or
we get an ABBA deadlock

the problem was that the first database connection closing would
sometimes lead to the database being deleted before the other
connections got going

Fix TestClearReferences

TestClearReferences currently fails because the fields in
LocalDateTimeUtils are not final.

mostly because various tests fail in (mvStore && !mvcc) mode, was
previously hidden by the fact that we did not test that combination,
despite it being our default mode

so we don't use up too much in the way of Travis/CI resources

Also don't bother testing MVCC mode, since that's going to go away at
some point, and it's certainly not a default setting for us

turn off partial writes in TestReorderWrites for now, there is a bug
causing massive memory usage increases (for some reason, only when the
test is run in the context of TestAll)

found by running TestRandomSQL for long periods of time

Added BITGET function

Migrate to Travis container-based infrastructure

Sine we're not using sudo we can migrate to the container-based Travis
build infrastructure [1]. This has the following advantages:

 - Builds start in seconds
 - More available resources
 - Better network capacity, availability and throughput
 - Caching available for open source projects

The builds will still fail due to an `OutOfMemoryError` but that's a
different issue.

 [1] https://docs.travis-ci.com/user/migrating-from-legacy/