mount: Add test coverage for RecursiveUnmount

[thaJeztah]

While there's tests for functions used by this function (GetMounts(), Unmount()), there's currently no test coverage for RecursiveUnmount(). We could use some test coverage for this function.

Opening this as a tracking issue, and adding the "help wanted" label, in case someone wants to work on this (please comment below if you want to work on this!)

/cc @kolyshkin

[kolyshkin]

This is partially addressed by #64.

[manugupt1]

@thaJeztah can we close this now?

[kolyshkin]

Yes, I think this is now addressed by #64 and #107.