Add ignoreline and includeline options to check-disk.rb

This is basically a modified version of check-disk.rb in PR #280 with additional functionality, differences being:
* `-l` allows multiple (comma-separated) patterns to ignore from df output
* `-L` allows multiple patterns of df output to **only** include (mutually-exclusive with `-l`)
* both options above use regex matches so you can use wildcards, anchors, etc.
* `-d, --debug` option shows df output for testing purposes

This could potentially eliminates the need for some of the pre-existing options, however I left them in for backwards compatibility.