Improvements in neutron_test sanity tests script

Neutron test 'sanity' script was fixed and cleanup functionality was added, to
allow a complete test cycle for create/update/delete methods.

Change-Id: I4f611f68c100356a672dac0851d7339736c73f71
Closes-Bug: #1274945
Merge "Improvements in neutron_test sanity tests script"