Add 'teardown' action to virtualbmc-domain role

ansible/roles/virtualbmc-domain/README.md

@@ -1,7 +1,9 @@
 Virtual BMC Domain
 ==================
 
-This role ensures a Libvirt domain is added to and started in Virtual BMC.
+This role configures a Libvirt domain in Virtual BMC. If `vbmc_state` is
+`present`, it will ensure the domain is added and started; if `vbmc_state` is
+`absent`, it will ensure the domain is stopped and deleted.
 
 Requirements
 ------------
@@ -22,3 +24,5 @@ Role Variables
 - `vbmc_ipmi_password`: The IPMI password that Virtual BMC will use.
 - `vbmc_log_directory`: The directory in which to store Virtual BMC logs. If
    not overridden from `None`, output will not be logged to a file.
+- `vbmc_state`: Whether the domain should be `present` or `absent` in Virtual
+  BMC. Defaults to `present`.

ansible/roles/virtualbmc-domain/defaults/main.yml

@@ -13,3 +13,5 @@ vbmc_domain:
 vbmc_log_directory:
 # The path to the virtualenv in which Virtual BMC is installed.
 vbmc_virtualenv_path:
+# Whether the domain should be `present` or `absent` in Virtual BMC.
+vbmc_state: present

ansible/roles/virtualbmc-domain/tasks/main.yml

@@ -45,6 +45,7 @@
       --username '{{ vbmc_ipmi_username }}'
       --password '{{ vbmc_ipmi_password }}'
       --address {{ vbmc_ipmi_address }}
+  when: vbmc_state == 'present'
   become: true
   tags:
     - skip_ansible_lint
@@ -56,6 +57,7 @@
   # Retry a few times in case the VBMC daemon has been slow to process the last
   # few commands.
   until: res is succeeded
+  when: vbmc_state == 'present'
   become: true
   tags:
     - skip_ansible_lint