[Finder] Shell escape and windows support

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

Add escaping of command passed to Shell::testCommand().
Fix todo add support for windows.
agree i will change it `which` is available under suse, ubuntu, debian, fedora, bsd