improve ut coverage of conductor/vnflcm_driver related files

Currently, UT coverage of tacker is 68% in average, some new features like kubernetes-driver, new db objects, and some core features like tacker server and tacker conductor is still not full covered by UT yet.

This blueprint is aim to improve Tacker-conductor/Vnflcm-driver related files' UT coverage over 90%. Since tacker has large amout of code, in this blueprint, it is better to complete improvement by feature in step. The blueprint will include these files:

* Tacker-conductor(current coverage)
  tacker/conductor/conductor_server.py 72%
  tacker/common/container/kubernetes_utils.py 71%
  tacker/conductor/conductorrpc/vim_monitor_rpc.py 0%

* Vnflcm-driver(current coverage)
    tacker/vnflcm/vnflcm_driver.py 57%

Target :
  * over 90% test coverage
     * codes not called/not in functions will not in UT code, but are calculated as not coverd.
        Thus some file cannot reach 90% coverage.
  * cover all non-internal methods
  * merge in Wallaby