Remove variable part of agent dict to fix AgentManagementTest

Agents may vary their configuration while API tests blindly
compare agent dicts. Need to pop items that may change.

Change-Id: I150f4e9f2e79f6e20f18dee69cf061c68a5bed68
Closes-Bug: #1299350
fix import for default clients in clients.py

All default clients will be imported in clients.py even
if the services are disabled in tempest.conf. That will
cause import error when run tests. This patch moves the
import statements into relevant functions.

Closes-Bug: #1307323

Change-Id: I1260cceb2821400eb42959cb701e40ae449dd452
Merge "fix import for default clients in clients.py"
Merge "Remove variable part of agent dict to fix AgentManagementTest"