Fix Mule inbound endpoint leak - EUCA-7810

MuleClient is extended to override the default endpoint access to avoid
leaking an endpoint per request sent.

The eucalyptus service mule configuration is updated to add a
synchronous endpoint for VM transport (internal). The creation of a new
synchronous endpoint was previously hiding this issue.

EUCA-7810
Merge remote-tracking branch 'origin/dev/sjones/EUCA-7810' into testing