Add swift discoverable_api support to verify_tempest_config

This commit adds support to the verify_tempest_config.py script
for detecting which swift apis are enabled.

Partially implements bp config-verification

Change-Id: I7f4a1fdc41246b3584aa5d3faca5920ca5c2f6e5
Merge "Add swift discoverable_api support to verify_tempest_config"