Refactor BDD test scenarios of OpenStack to stabilize testing behavior

Problem/Motivation

As creating/deleting a resource takes time, the following test scenarios often fails due to timing issue.

• Creating a snapshot as the volume is still creating.
• Terminating a launch template as the instance keeps running or being stopped.

Proposed resolution

Break the current scenario into two scenarios to make sure each step.

This patch also includes a temporary workaround by avoid no error check on creating a launch template.