Use ConfigParser to generate tempest config

Usage of ConfigParser provides flexible way to generate various
configuration files for tempest.
Generation of a configuration file takes a time, so checking the
existence of a file is moved into function `verify`.

Blueprint tempest-verification
Closes-Bug: #1296769

Change-Id: I221bf18090e93eb66a84dc80b87c80a0d1deb99a
Merge "Use ConfigParser to generate tempest config"