(PUP-1628) Fix mount provider for AIX

The way that AIX tracks its mounted filesystems is different than other
unix or linux operatingsystems. AIX uses /etc/filesystems and has
entirely different filesystem options.

This commit takes advantage of two parsedfile hooks, post_parse and
to_line, to read & generate /etc/filesystem entries. Parsedfile was
not created with arbitrary-ordering in mind, and any /etc/filesystem
entries will have their attributes reordered by to_line

Options in AIX without related properties in Puppet's mount type are
placed under the "options" property.

The specs I wrote for instances work, but there are many other failures
when running specs on AIX. This PR doesn't include specs for to_line