common/config_test.go:
Replaced instances of os.Mkdir and os.Create with tests that use
the existing "common/test-fixtures" mechanism.
Removed the runtime.GOOS test for the "FileExistsLocally" test,
as the functionality should work regardless of the platform.
Added some more comprehensive tests for the relative uri/pathing.
Replaced the Windows Object Manager name test as the Object
Manager's naming scheme is different from a UNC path.
Modified the FilePaths tests to support the policy of windows absolute
paths being prefixed with the `/` introduced with PR #5761.