add -piggyack parameter to control activity submission in the pool benchmark
close context if not in use (pool benchmark)
Merge branch 'master' of github.com:Microsoft-CISL/REEF into sergiym_pool_piggyback
code review fix: move code for building the activity configuration into a common method.
Merge branch 'master' of github.com:Microsoft-CISL/REEF into sergiym_pool_piggyback
Merge pull request #659 from Microsoft-CISL/sergiym_pool_piggyback

Add -piggyback parameter to the Pool benchmark