Respect the rw/ro kernel cmdline option.

Also pipe the zpool list failure to /dev/null.
Merge pull request #19 from clefru/initcpio-readonly-mount

Respect the rw/ro kernel cmdline option.
Merge pull request #20 from graysky2/master

3.13.7 update
Merge pull request #1 from demizer/master

sync up with demizer