tests/qemu-iotests: add bitmap resize test 246

Test that we can actually resize qcow2 images with persistent bitmaps
correctly. Throw some other goofy stuff at the test while we're at it,
like adding bitmaps of different granularities and at different times.

Signed-off-by: John Snow <jsnow@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Tested-by: Eric Blake <eblake@redhat.com>
Message-id: 20190311185147.52309-5-vsementsov@virtuozzo.com
   [vsmentsov: drop \n from the end of test output,
      test output changed a bit: some bitmaps goes in other order
      int the output]
Signed-off-by: John Snow <jsnow@redhat.com>