Update mongodb plugins

* Update mongodb plugins
* fix category
* chmod +x
* flake8-CI
* flake8 adjustments for mongo_collection_ and env python3

plugins/mongodb/mongo_btree

@@ -1,6 +1,22 @@
-#!/usr/bin/python
+#!/usr/bin/env python
+"""
+=head1 NAME
+    MongoDB btree Plugin
 
-## GENERATED FILE - DO NOT EDIT
+=head1 APPLICABLE SYSTEMS
+
+    Works until MongoDB 2.7. The "indexCounters" field was removed in 2.8 version.
+
+=head1 CONFIGURATION
+
+    [mongo_btree]
+    env.MONGO_DB_URI mongodb://user:password@host:port/dbname
+
+=head1 AUTHOR
+
+    Original script there : https://github.com/comerford/mongo-munin
+    Doc added by Alban Espie-Guillon <alban.espie@alterway.fr>
+"""
 
 import urllib2
 import sys
@@ -50,5 +66,3 @@ if __name__ == "__main__":
         doConfig()
     else:
         doData()
-
-