[1 of 5] util: Move CheckDiskSpace to util.

Summary:
partial PR15118 backport
https://github.com/bitcoin/bitcoin/pull/15118/commits/62e7addb632cad77cbd5fbccbaee51c7b32505d0

Test Plan: make check

Reviewers: deadalnix, Fabien, jasonbcox, #bitcoin_abc

Reviewed By: jasonbcox, #bitcoin_abc

Maniphest Tasks: T631

Differential Revision: https://reviews.bitcoinabc.org/D3585