Fixing the config/config_test, the discovery/file/file_test and the
promql/promql_test tests for Windows. For most of the tests, the fix involved
correct handling of path separators. In the case of the promql tests, the
issue was related to the removal of the temporal directories used by the
storage. The issue is that the RemoveAll() call returns an error when it
tries to remove a directory which is not empty, which seems to be true due to
some kind of process that is still running after closing the storage. To fix
it I added some retries to the remove of the temporal directories.
Adding tags file from Universal Ctags to .gitignore
