(#8663) Disable spec tests for unsupported functionality on Windows

The mount, shell, and ssh_authorized_key types are not supported on
Windows, so these spec tests have been disabled when running on
Windows.

One of the compiler spec tests fails on Windows because
Puppet::Util.execute attempts to execute a program named "git rev-parse
HEAD". This has different semantics than Unix, where the command is
splatted, Kernel.exec(*command). Since this truly is a Windows bug, I
removed the fails_on_windows tag and updated ticket #8410.

Reviewed-by: Jacob Helwig <jacob@puppetlabs.com>
(cherry picked from commit d9ce88d10707268fe41c8f3ad1166137fe8e202f)