Adds ExternalIpAddressExhaustedClient exception

Adds the ExternalIpAddressExhaustedClient exception so
a more specific exception than NeutronClientException is raised
when IPs run out. This will allow for better exception
handling in Nova.

Closes-Bug: 1233143

Change-Id: I9f40bf14eec0f485dfd21b36605a2474b99a8941
Forcibly clear connection pool after every request

Neutron client is ending up with bad socket descriptors
which causes the behavior including trying to read from
the socket that amqp currently holds etc. A temporary
solution is to clear the connection pool so we get a
fresh socket built for every request.

Closes-Bug: 1229475

Change-Id: I43b1fe535bc5bd1fc726c97a293bf7912cd7ef1e
Merge "Forcibly clear connection pool after every request"
Merge "Adds ExternalIpAddressExhaustedClient exception"