[scripts][main_cli] Add extra function to logger

This leads to a crash. Originally in beat.py, but forgot to move it in
main_cli.py.

beat/cmdline/scripts/main_cli.py

@@ -8,6 +8,16 @@ from click_plugins import with_plugins
 from .click_helper import verbosity_option
 from ..config import Configuration
 
+# defines our own logging level for extra information to be printed
+logging.EXTRA = 15
+logging.addLevelName(logging.EXTRA, "EXTRA")
+
+def _extra(self, message, *args, **kws):
+    if self.isEnabledFor(logging.EXTRA):
+        self._log(logging.EXTRA, message, args, **kws)
+
+logging.Logger.extra = _extra
+
 @with_plugins(pkg_resources.iter_entry_points('beat.cli'))
 @click.group()
 @click.option('-T', '--test-mode', help='Assume test mode and doesn\'t setup '