fixed Python 3 keys() usage (#1861) (#1890)

* fixed python3 keys()

* added changelog fragment

* Update plugins/modules/cloud/spotinst/spotinst_aws_elastigroup.py

Co-authored-by: Felix Fontein <felix@fontein.de>

* Update plugins/cache/redis.py

Co-authored-by: Felix Fontein <felix@fontein.de>

* rolledback redis.py per PR

* Update plugins/modules/monitoring/sensu/sensu_check.py

Co-authored-by: Felix Fontein <felix@fontein.de>

* removed unnecessary ignore lines

* adding memcached and one case in redis is indeed necessary

* Update changelogs/fragments/1861-python3-keys.yml

Co-authored-by: Felix Fontein <felix@fontein.de>

* Update changelogs/fragments/1861-python3-keys.yml

* Update changelogs/fragments/1861-python3-keys.yml

Co-authored-by: Felix Fontein <felix@fontein.de>

Co-authored-by: Felix Fontein <felix@fontein.de>
(cherry picked from commit 434f383ae9)

Co-authored-by: Alexei Znamensky <103110+russoz@users.noreply.github.com>

scripts/inventory/nsot.py

@@ -181,7 +181,7 @@ class NSoTInventory(object):
                     sys.exit('%s\n' % e)
         else:  # Use defaults if env var missing
             self._config_default()
-        self.groups = self.config.keys()
+        self.groups = list(self.config.keys())
         self.client = get_api_client()
         self._meta = {'hostvars': dict()}