Add TestRunner class, which will run tests in a new python iotests
running framework.

There are some differences with current ./check behavior, most
significant are:
- Consider all tests self-executable, just run them, don't run python
  by hand.
- Elapsed time is cached in json file
- Elapsed time precision increased a bit
- Instead of using "diff -w" which ignores all whitespace differences,
  manually strip whitespace at line end then use python difflib, which
  no longer ignores spacing mid-line

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210125185056.129513-5-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>