[FEATURE REQUEST] additional disk and mount functionality

[nicholasmhughes]

Describe the solution you'd like

• function that will return the filesystem type for a path
• function that will return the underlying block device for a path.

Describe alternatives you've considered

• the mount.active function provides a data structure showing this information for all mounts, but it'd be nice to not have to pick through that.
• the disk.fstype function can provide a filesystem type for a given device, but there isn't an easy way to determine which mount corresponds to a given path... and then we're back to picking through the mount.active output to determine the device

Please Note
If this feature request would be considered a substantial change or addition, this should go through a SEP process here https://github.com/saltstack/salt-enhancement-proposals, instead of a feature request.