avocado.core.plugins.multiplexer: Style fix

sort imports alphabetically.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

avocado/core/plugins/multiplexer.py

@@ -14,11 +14,11 @@
 
 import sys
 
-from . import plugin
-from .. import output
+from .. import multiplexer
 from .. import exit_codes
+from .. import output
 from .. import tree
-from .. import multiplexer
+from . import plugin
 
 
 class Multiplexer(plugin.Plugin):