Added Constants.Explore.START_ON_DEMAND config option
Use Constants.Explore.START_ON_DEMAND to speedup TestBase startup and shutdown
Addressed comments
Addressed comments and added startOnDemand to ExploreExecutorHttpHandler
Start on demand in BaseHiveExploreService instead
Addressed comments
Merge pull request #543 from caskdata/feature/speedup-testbase

CDAP-86 Improve TestBase startup and shutdown time