Set better understandable report titles and mail subject line

This commit aims to provide the same effect w.r.t report html title
and mail subject to describe the setup, as was being done in newer
contrail-test infra on master branch

Also moved initialization of ContrailTestInit class attributes to
_init_vars() method

Change-Id: If1143d40a5fb3787913c8db8e8ff1b6c85c746ae