Fix default value of "ignore_req_list" config option

If audit is enabled ironic API service does not start with default
value (None) of "ignore_req_list" config option. This patch changes
default value to empty string. Related modification added to ironic
sample config.

Closes-Bug: 1648387
Change-Id: Ifbbbed4012670b4b05fcf63e5586024f3c927875

etc/ironic/ironic.conf.sample

@@ -663,7 +663,7 @@
 # be done on any GET or POST requests if this is set to
 # "GET,POST". It is used only when API audit is enabled.
 # (string value)
-#ignore_req_list = <None>
+#ignore_req_list =
 
 
 [cimc]

ironic/conf/audit.py

@@ -26,6 +26,7 @@ opts = [
                       'Used only when API audit is enabled.')),
 
     cfg.StrOpt('ignore_req_list',
+               default='',
                help=_('Comma separated list of Ironic REST API HTTP methods '
                       'to be ignored during audit logging. For example: '
                       'auditing will not be done on any GET or POST '

releasenotes/notes/bug-1648387-92db52cbe007fabd.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - Fixes the issue that API service does not start if audit is enabled with
+    default value of "ignore_req_list" config option.