Add fly:bats rake task for running BATs from a local branch #2991

Job	Run time
unit_specs (release:parallel)	1m 42s
unit_specs-director (mysql)	6m 9s
unit_specs (common:parallel)	1m 36s
unit_specs (monitor:parallel)	1m 53s
unit_specs (nats_sync:parallel)	1m 51s
unit_specs (integration_support:parallel)	1m 45s
unit_specs-director (postgresql)	4m 24s
	19m 20s

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