Add ANSIBLE_CONFIG to system container installer

The provided configuration file was not being honored. This change adds
a new variable called ANSIBLE_CONFIG which points to the ansible.cfg
file within the container. By default it is set to the configuration
provided by openshift-ansible within the container at:

    /usr/share/ansible/openshift-ansible/ansible.cfg

images/installer/system-container/root/exports/config.json.template

@@ -21,7 +21,8 @@
             "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
             "TERM=xterm",
             "OPTS=$OPTS",
-            "PLAYBOOK_FILE=$PLAYBOOK_FILE"
+            "PLAYBOOK_FILE=$PLAYBOOK_FILE",
+            "ANSIBLE_CONFIG=$ANSIBLE_CONFIG"
         ],
         "cwd": "/opt/app-root/src/",
         "rlimits": [

images/installer/system-container/root/exports/manifest.json

@@ -6,6 +6,7 @@
         "VAR_LOG_OPENSHIFT_LOG": "/var/log/ansible.log",
         "PLAYBOOK_FILE": "/usr/share/ansible/openshift-ansible/playbooks/byo/config.yml",
 	"HOME_ROOT": "/root",
+	"ANSIBLE_CONFIG": "/usr/share/ansible/openshift-ansible/ansible.cfg",
         "INVENTORY_FILE": "/dev/null"
     }
 }