Replace os.getlogin

... according to the recommendation in the python documentation.

pifpaf/drivers/mysql.py

@@ -10,8 +10,8 @@
 # implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import getpass
 import logging
-import os
 
 from pifpaf import drivers
 
@@ -27,7 +27,7 @@ def _setUp(self):
         os.mkdir(datadir)
         os.mkdir(tempdir)
 
-        mysql_user_to_use = os.getlogin()
+        mysql_user_to_use = getpass.getuser()
 
         c, _ = self._exec(["mysqld",
                            "--no-defaults",