Add ability to reuse existing OpenStack set-up

Add ability to reuse existing OpenStack set-up

This change adds two optional flags to the context configuration for heat:
* no_setup -- to re-use an existing OpenStack deployment
* no_teardown -- to skip undeploying the context, so it is available in other testcases

In order to achieve this, resource naming had to be made more predictable.
When no_setup or no_teardown are set:
* Do not add a suffix to context name
* When searching, try with and without a suffix to find a server by name

All behaviors remain the same unless these values are set.

NOTE:
  This feature doesn't work with the NSPerf scenario, because the
  interfaces in the VNFs are bound to DPDK after the first test, so the
  look-up for missing topology information fails in subsequent test
  runs, as the interfaces are not visable to the kernel.
  This can be addressed either by either unbinding the interfaces from
  DPDK at the end of each test, or modifying the look-up for the missing
  topology information to query DPDK as well.
  The change will be made in a future patch.

JIRA: YARDSTICK-886
Change-Id: I6df5e86e419c283a2bee41917e4f62179aa9c31a
Signed-off-by: Emma Foley <emma.l.foley@intel.com>