Changes to ensure delete_containers is done at class level tear down

  Invoking delete containers at test level tearDown caused:
1) unnecessary requests are being sent again in the tearDown for
the subsequent methods,
2) possible race condition can happen between methods during the
tearDown.

Closes-Bug: #1938593

Change-Id: I24087607a9f0129b7b3d21473196fab1b5f08cd4
4 files changed