bring back test_parallel_do

[tonyyang-svail]

Currently, test on parallel_do_op is disabled. Need to bring it back.

Paddle/python/paddle/v2/fluid/tests/test_parallel_op.py

Lines 18 to 20 in b8a1798

	import sys
	# TODO(dzhwinter): get places op check need to be enhanced.
	sys.exit(0)