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>
Merge pull request #244 from ceph/wip-7199-wusui

Wip 7199 wusui
Revert "valgrind.supp: be less picky about library versions"

This reverts commit f895d16c9e2fd59aab446254e53480cdb91092a1.
valgrind: fix tcmalloc suppression for trusty

Fixes: #8225
Signed-off-by: Sage Weil <sage@inktank.com>