(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.
Maybe we should create a function for these. All the CMake scripts are pretty much copy and paste.