Limit neutron API calls
Limit neutron API calls

1. Fix storing attribute in cache by MAC
2. Do not update node when MAC is found in the cache it has
   already been updated
3. Store not found MACs in cache so that no more calls to neutron
   are made on following node updates

Refs #116

Change-Id: I1482d0e3a32c3d819695e72493d89de03e3a9998
Reviewed-on: http://softwarefactory-project.io/r/4936
Reviewed-by: Sylvain Afchain <b9baee1c2e4cc202620c6529e0c0bd3dbc38b6dc@gmail.com>
Tested-by: Sylvain Afchain <b9baee1c2e4cc202620c6529e0c0bd3dbc38b6dc@gmail.com>
Workflow: Sylvain Afchain <b9baee1c2e4cc202620c6529e0c0bd3dbc38b6dc@gmail.com>
Tested-by: Jenkins CI <d95b56ce41a2e1ac4cecdd398defd7414407cc08@softwarefactory-project.io>

safchain/skydive,skydive-project/skydive,lebauce/skydive,safchain/skydive,safchain/skydive,lebauce/skydive,skydive-project/skydive,safchain/skydive,lebauce/skydive,safchain/skydive,skydive-project/skydive,redhat-cip/skydive,skydive-project/skydive,safchain/skydive,lebauce/skydive,redhat-cip/skydive,lebauce/skydive,safchain/skydive,lebauce/skydive,redhat-cip/skydive,skydive-project/skydive,safchain/skydive,lebauce/skydive,lebauce/skydive,skydive-project/skydive,skydive-project/skydive