Merge pull request #1579 from edx/cg/add_security_fixes

Update security check to be smarter

playbooks/roles/common/tasks/security-ubuntu.yml

 
-- name: Apply bash security update
+- name: Check if we are vulnerable
+  shell: executable=bash env x='() { :;}; echo vulnerable'  bash -c "echo this is a test"
+  register: test_vuln
+
+- name: Apply bash security update if we are vulnerable
   apt: name=bash state=latest update_cache=true
+  when: "'vulnerable' in test_vuln.stdout"
 
-- name: Check and fail if we are still vulnerable
+- name: Check again and fail if we are still vulnerable
   shell: executable=bash env x='() { :;}; echo vulnerable'  bash -c "echo this is a test"
+  when: "'vulnerable' in test_vuln.stdout"
   register: test_vuln
   failed_when: "'vulnerable' in test_vuln.stdout"