Restrict the length of bay's name to avoid passing a invalid long name
to heat stack.
Reason of 242 is:
stack_name = '%s-%s' % (bay.name, short_id.generate_id())
255 - len(short_id.generate_id()) - 1 = 242
Closes-bug: #1606785
Change-Id: If22a9018ece718f014c40e8059b945ae1a411f5b