Allow more strings in filters

A comma separated list can now be used in filter and filter-out.

Fixes: #9925
Signed-off-by: Warren Usui <warren.usui@inktank.com>
More suite filter changes.

Comment change, and update help message to reflect the ability to
use a comma separated list as a filter.
Merge pull request #351 from ceph/wip-9925-wusui

Allow more strings in filters