Add expensive tests selection option flag
Add tests filtering support to only run a set of tests
Move `SaltClientTestCaseMixIn` from `salttesting.case` to `salttesting.mixins`
Move `ShellCaseCommonTestsMixIn` from `salttesting.case` to salttesting.mixins`
Remove unused import
Remove stray print and add backwards compatible imports
Don't import twice and stop PyLint's complaints