Shutdown cron asynchronously

Testing Done:
./gradlew build

Bugs closed: AURORA-325

Reviewed at https://reviews.apache.org/r/20425/
AURORA-299: use system thrift if available

Updates gradle bootstrapThrift to use a system installed Thrift if available
and if it is the same version we are currently using.

Testing Done:
ran build with and without Thrift installed

Bugs closed: AURORA-299

Reviewed at https://reviews.apache.org/r/20246/
AURORA-267: Add container to popover to avoid clipping issue

Reviewed at https://reviews.apache.org/r/20344/
Work in progress on using H2 + MyBatis.