Speed up metadata server registration

Speed up metadata server registration

If heat-engine and heat-metadata were started at approximately the same
time, such that heat-engine was not ready to receive the registration call
from heat-metadata on the first attempt, it would take a minute before the
next retry. Instead, start with a very short timeout (2s) and increase it
if the engine does not show up.

Fixes #159

Change-Id: Ie2efcce667f1dde9ae227a4bb19a1d6a2b7cf135
Signed-off-by: Zane Bitter <zbitter@redhat.com>