Ansible launcher: import get_exception in ansible command

The ansible command module was missing this import statement.

Change-Id: I456512a2a7f2138ac78eb8594c8808f664a9506f
diff --git a/zuul/ansible/library/command.py b/zuul/ansible/library/command.py
index 97bdb27..84c3715 100644
--- a/zuul/ansible/library/command.py
+++ b/zuul/ansible/library/command.py
@@ -116,6 +116,7 @@
 import threading
 
 from ansible.module_utils.basic import AnsibleModule, heuristic_log_sanitize
+from ansible.module_utils.basic import get_exception
 # ZUUL: Hardcode python2 until we're on ansible 2.2
 from ast import literal_eval