Add multiple server actions fixtures in Stacktach

* Moved stacktach db api calls to a common method
  stacktach_events_for_server() in StackTachDBFixture
  and removed all Stacktach specific fixtures.
* Removed various fixtures for multiple server actions and
  made them into methods under one mixture for adding
  stacktach functional tests.
* This fixture has methods which does multiple server actions
  like create, delete, rebuild, reboot, resize, change password, etc.
* Then pull up launches, exists & deletes details for the server
  from Stacktach using DB APIs.
* Fixed param names to be not in Camel case
* Changed adminPass to admin_pass
* Renamed methods to create_and_action*

Change-Id: I85161b152959d47e62a73a1ebdd77145b36969a0
Merge "Add multiple server actions fixtures in Stacktach"