* Replace .testr.conf by .stestr.conf for migration and update
.gitignore, test-requirements.txt and lower-constraints.txt
files accordingly
* Use py3 as the default runtime and 3.18.0 as the minversion
for tox
* Add group_regex to run all tests
Signed-off-by: HeroicHitesh <email.hiteshkumar@gmail.com>
Change-Id: I704356082e2c25d21aff3c5433efa077259b0b1d
