The swarm func test occasionally failed with the error below. This
error cannot be determinately reproduced. After some experiments,
it seems that swarm will abort connections during registration of
a new swarm agent.
ConnectionError: ('Connection aborted.', BadStatusLine("''",))
This commit tries to fix the issue by waiting for the completion of
agent registration. After the swarm agent service starts, it checks
ETCD to ensure the agent was successfully registered before sending
signal to Heat to indicate its success.
Closes-Bug: #1521395
Change-Id: Iec1772d1df7d85e367676758b1f97a5b604c0eb7
8733cd37fa