Split up the travis run into a unit-test shard and multiple IT shards.

Also move tests/python/pants_test/tasks/jvm_compile/java:test_java_compile_integration
out of the unit test suite.

Testing Done:
CI went green here: https://travis-ci.org/pantsbuild/pants/builds/40216412

Bugs closed: 773

Reviewed at https://rbcommons.com/s/twitter/r/1290/
Sync of https://github.com/pantsbuild/pants/commit/92901321dfed0470ed795bbed4bf0f4c4d1a9c86