facter grain facter_blockdevices: should be parsed to a list

[ghost]

The facter grains facter_blockdevices, facter_filesystems and facter_interfaces would be much more useful if the comma separated values would be parsed to a list :)

Currently they are strings where the values are separated by comma only:

    facter_blockdevices:
        sda,sr0
    facter_interfaces:
        eth0,lo,tun0
    facter_filesystems:
        btrfs,ext2,ext3,ext4