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: Ifb78bfae3748ed8c0954e761a624c87884fe48c6

meta/main.yml

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

tasks/swift_install.yml

@@ -39,45 +39,15 @@
   retries: 5
   delay: 2
 
-- name: Get local venv checksum
-  stat:
-    path: "/var/cache/{{ swift_venv_download_url | basename }}"
-    get_md5: False
-  when:
-    - not swift_pypy_enabled | bool
-    - not swift_developer_mode | bool
-  register: local_venv_stat
-
-- name: Get remote venv checksum
-  uri:
-    url: "{{ swift_venv_download_url | replace('tgz', 'checksum') }}"
-    return_content: True
-  when:
-    - not swift_pypy_enabled | bool
-    - not swift_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: "{{ swift_venv_download_url }}"
     dest: "/var/cache/{{ swift_venv_download_url | basename }}"
-    force: yes
-  failed_when: false
-  register: get_venv
+    checksum: "sha1:{{ lookup('url', swift_venv_download_url | replace('tgz', 'checksum')) }}"
+  register: swift_get_venv
   when:
     - not swift_pypy_enabled | bool
     - not swift_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 swift get_venv fact
-  set_fact:
-    swift_get_venv: "{{ get_venv }}"
 
 - name: Remove existing venv
   file:
@@ -121,7 +91,7 @@
   delay: 2
   when:
     - not swift_pypy_enabled | bool
-    - swift_get_venv | failed or swift_developer_mode | bool
+    - swift_developer_mode | bool
   notify:
     - Restart swift services
 
@@ -131,7 +101,7 @@
   when:
     - not swift_pypy_enabled | bool
     - not swift_developer_mode | bool
-    - swift_get_venv | success
+    - swift_get_venv | changed or swift_venv_dir | changed
 
 - include: swift_pypy_setup.yml
   static: no