thrashosds: try ceph-objectstore-tool for 10 minutes

thrashosds: try ceph-objectstore-tool for 10 minutes

If ceph-objectstore-tool binary is not present, it's likely because we're in
the middle of an upgrade. Do not try to run the binary until we verify that
it's really present. If it is absent, spend up to 10 minutes waiting for it to
appear.

Before this patch there was quite a large window for a race to occur. This
patch doesn't entirely eliminate it, but drastically reduces it.

Fixes: http://tracker.ceph.com/issues/18014
Signed-off-by: Nathan Cutler <ncutler@suse.com>