Use updated get_url module checksum functionality

Starting in Ansible 2.0, the get_url [1] module provides the
ability for a checksum to be provided to the get_url module
which will be verified against the local destination file
and the task skipped if it matches.

[1] http://docs.ansible.com/ansible/get_url_module.html

This patch implements the use of this functionality.

The ability to ignore a venv download failure is also removed
as this is not necessary or desirable. It is better for the
download to fail and the playbook execution to stop immediately
so that the failure point is exposed.

Change-Id: I0e33da0dc601eaa4af06c03a20803fcd01405531

meta/main.yml

@@ -18,7 +18,7 @@ galaxy_info:
   description: Installation and setup of horizon
   company: Rackspace
   license: Apache2
-  min_ansible_version: 1.9
+  min_ansible_version: 2.0
   platforms:
     - name: Ubuntu
       versions:

tasks/horizon_install.yml

@@ -39,49 +39,19 @@
   retries: 5
   delay: 2
 
-- name: Get local venv checksum
-  stat:
-    path: "/var/cache/{{ horizon_venv_download_url | basename }}"
-    get_md5: False
-  when:
-    - not horizon_developer_mode | bool
-  register: local_venv_stat
-
-- name: Get remote venv checksum
-  uri:
-    url: "{{ horizon_venv_download_url | replace('tgz', 'checksum') }}"
-    return_content: True
-  when:
-    - not horizon_developer_mode | bool
-  register: remote_venv_checksum
-
-# TODO: When project moves to ansible 2 we can pass this a sha256sum which will:
-#       a) allow us to remove force: yes
-#       b) allow the module to calculate the checksum of dest file which would
-#          result in file being downloaded only if provided and dest sha256sum
-#          checksums differ
 - name: Attempt venv download
   get_url:
     url: "{{ horizon_venv_download_url }}"
     dest: "/var/cache/{{ horizon_venv_download_url | basename }}"
-    force: yes
-  failed_when: false
-  register: get_venv
-  when:
-    - not horizon_developer_mode | bool
-    - (local_venv_stat.stat.exists == False or
-        {{ local_venv_stat.stat.checksum is defined and local_venv_stat.stat.checksum != remote_venv_checksum.content | trim }})
-
-- name: Set horizon get_venv fact
-  set_fact:
-    horizon_get_venv: "{{ get_venv }}"
+    checksum: "sha1:{{ lookup('url', horizon_venv_download_url | replace('tgz', 'checksum')) }}"
+  register: horizon_get_venv
+  when: not horizon_developer_mode | bool
 
 - name: Remove existing venv
   file:
     path: "{{ horizon_bin | dirname }}"
     state: absent
-  when:
-    - horizon_get_venv | changed
+  when: horizon_get_venv | changed
 
 - name: Create horizon venv dir
   file:
@@ -116,8 +86,7 @@
   until: install_packages|success
   retries: 5
   delay: 2
-  when:
-    - horizon_get_venv | failed or horizon_developer_mode | bool
+  when: horizon_developer_mode | bool
   notify: Restart apache2
 
 - name: Update virtualenv path
@@ -125,7 +94,7 @@
     virtualenv-tools --update-path=auto {{ horizon_bin | dirname }}
   when:
     - not horizon_developer_mode | bool
-    - horizon_get_venv | success
+    - horizon_get_venv | changed or horizon_venv_dir | changed
 
 - name: Create horizon link for venv
   file: