(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.
This could be insert, which saves some code and a tree walk. Insert doesn't modify the map if the key already exists.