Update unit test for Cluster.__repr__()

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Post last_in_suite jobs, but delete when run

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Only attempt to use sudo if necessary
Allow scrubbing while thrashing

Added ability to implement scrubbing while thrashing
(scrub_interval in config can be set to an interval
similar to how clean_interval is set).  Defaults to 0,
which indicates that no scrubbing will take place.
Add scrub_interval description to thrashosds docstring.

Fixes: 7199
Signed-off-by: Warren Usui <warren.usui@inktank.com>