Require cask `osxfuse`

[Amar1729]

as of early 2021 homebrew-core no longer ships osxfuse due its change in licensing, but it is provided by homebrew-cask.

Some reference boilerplate code for homebrew taps that depend on osxfuse functionality:

• https://github.com/gromgit/homebrew-fuse
• https://github.com/borgbackup/homebrew-tap/blob/875dc6ff646b0ad48986f9f327ff59ed279a6199/Formula/borgbackup-fuse.rb

This should be added to libguestfs (all versions).

• [x] Done for 1.32 https://github.com/Amar1729/homebrew-libguestfs/commit/1dd2a1f1f9bbd594687f13cb3fca786f9c2eb09a
• [ ] 1.40 (that one still doesn't build/test yet)

[Amar1729]

Closing this - added 1.32 as libguestfs.rb in #8 , and included osxfuse. Updated versions will keep the osxfuse block.