Fix filter in list operations for apps

Change-Id: I48be17e09542c2dab96589dad2b0796f389dff7c
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/osmclient/cli_commands/app.py b/osmclient/cli_commands/app.py
index 98811fd..0a14510 100755
--- a/osmclient/cli_commands/app.py
+++ b/osmclient/cli_commands/app.py
@@ -182,6 +182,8 @@
 @utils.require_hostname
 @click.option(
     "--filter",
+    default=None,
+    multiple=True,
     help="restricts the list to the items matching the filter",
 )
 @print_output.output_option