RFE: Add option to filter checkers

[stanislavlevin]

It would be great to have the option which will filter source or check.
For example, I want to run all checkers, but skip "source": "ipahealthcheck.system.filesystemspace" or
"check": "FileSystemSpaceCheck".

[rcritten]

We discussed this but had difficulty specifying the syntax without it blowing up into an unreadable mess.

#59 may benefit as well as skipping expected failures would be beneficial (e.g. warnings that you don't care about).

[rcritten]

I think this is covered by dfc8cae in #176 which added an excludes section to the configuration file so some sources/checks/results can be skipped in the output.