Logging: update logging config to pass null as a string to oslo config

This PS updates the logging config to pass null as a string though to
the rendering engine, which is required to avoid things like `<no value>`
when base64 encoding output.

Change-Id: I04d6afbc693ec1adf560c7be15704c8b7434c08f
Signed-off-by: Pete Birley <pete@port.direct>

barbican/values.yaml

@@ -448,7 +448,7 @@ conf:
         - default
     logger_root:
       level: WARNING
-      handlers: null
+      handlers: 'null'
     logger_barbican:
       level: INFO
       handlers:

cinder/values.yaml

@@ -766,7 +766,7 @@ conf:
         - default
     logger_root:
       level: WARNING
-      handlers: null
+      handlers: 'null'
     logger_cinder:
       level: INFO
       handlers:

congress/values.yaml

@@ -381,7 +381,7 @@ conf:
         - default
     logger_root:
       level: WARNING
-      handlers: null
+      handlers: 'null'
     logger_congress:
       level: INFO
       handlers:

glance/values.yaml

@@ -265,7 +265,7 @@ conf:
         - default
     logger_root:
       level: WARNING
-      handlers: null
+      handlers: 'null'
     logger_glance:
       level: INFO
       handlers:

heat/values.yaml

@@ -482,7 +482,7 @@ conf:
         - default
     logger_root:
       level: WARNING
-      handlers: null
+      handlers: 'null'
     logger_heat:
       level: INFO
       handlers:

ironic/values.yaml

@@ -153,7 +153,7 @@ conf:
         - default
     logger_root:
       level: WARNING
-      handlers: null
+      handlers: 'null'
     logger_ironic:
       level: INFO
       handlers:

keystone/values.yaml

@@ -863,7 +863,7 @@ conf:
         - default
     logger_root:
       level: WARNING
-      handlers: null
+      handlers: 'null'
     logger_keystone:
       level: INFO
       handlers:

magnum/values.yaml

@@ -151,7 +151,7 @@ conf:
         - default
     logger_root:
       level: WARNING
-      handlers: null
+      handlers: 'null'
     logger_magnum:
       level: INFO
       handlers:

mistral/values.yaml

@@ -482,7 +482,7 @@ conf:
         - default
     logger_root:
       level: WARNING
-      handlers: null
+      handlers: 'null'
     logger_mistral:
       level: INFO
       handlers:

neutron/values.yaml

@@ -1489,7 +1489,7 @@ conf:
         - default
     logger_root:
       level: WARNING
-      handlers: null
+      handlers: 'null'
     logger_neutron:
       level: INFO
       handlers:

nova/values.yaml

@@ -1536,7 +1536,7 @@ conf:
         - default
     logger_root:
       level: WARNING
-      handlers: null
+      handlers: 'null'
     logger_nova:
       level: INFO
       handlers:

senlin/values.yaml

@@ -196,7 +196,7 @@ conf:
         - default
     logger_root:
       level: WARNING
-      handlers: null
+      handlers: 'null'
     logger_senlin:
       level: INFO
       handlers: