(CFACT-58) Implement file system facts for OSX and Linux.

Implementing the following OSX facts:

* mountpoints - a structured fact detailing each mount point on the system.
* filesystems - a string fact listing the mounted file systems.

Implementing the following Linux facts:

* mountpoints - a structured fact detailing each mount point on the system.
* filesystems - a string fact listing the file systems supported by the kernel.
* partitions - a structured fact detailing the block device partitions.
I was just noting it's existence, but it is a complex library. I don't think it'd be worth the extra complexity here.