Add --overcloud-ssh-username option to Tobiko InfraRed plugin

It adds the ability to specify custom tripleo.overcloud_ssh_username
option to tobiko.conf file.

This is needed for some downstream jobs that use a custom ssh user
rather than default one (heat-admin).

Change-Id: I42a8e2d294bbe21f127150d45670be0a540b9e2f

infrared_plugin/plugin.spec

@@ -129,6 +129,10 @@ subparsers:
             type: Value
             help: hostname or IP address to be used to connect to undercloud host
             ansible_variable: undercloud_ssh_hostname
+          overcloud-ssh-username:
+            type: Value
+            help: user name to be used to connect to TripleO Overcloud hosts
+            ansible_variable: overcloud_ssh_username
 
       - title: Run stage
         options:

roles/tobiko-configure/defaults/main.yaml

@@ -12,6 +12,7 @@ test_default_conf:
 
   tripleo:
     undercloud_ssh_hostname: "{{ undercloud_ssh_hostname }}"
+    overcloud_ssh_username: "{{ overcloud_ssh_username }}"
 
 test_log_debug: false
 
@@ -22,5 +23,6 @@ test_runner_timeout: 14400.
 stackrc_file: '{{ ansible_user_dir }}/overcloudrc'
 
 undercloud_hostname: '{{ groups.get("undercloud", []) | first | default("undercloud-0") }}'
-
 undercloud_ssh_hostname: ''
+
+overcloud_ssh_username: ''