Fix missing space in help text for caching option.
Fix missing space in help text for caching option.

There are C-Style string concatenations by juxtaposition in the
help texts and one line was missing a trailing space which caused
two sentences to run into each other.

Change-Id: I8df8a57b4d27de91945a54b6bd1da47cb6ab481f

noironetworks/heat,openstack/heat,noironetworks/heat,openstack/heat