Add a retry when downloading extensions

[LorenzoBettini]

Downloading extensions is very flaky and many of my playbooks fail very often with errors of the shape:

TASK [petermosmans.customize-gnome : Download GNOME Shell extensions] **********
  failed: [instance] ([email protected]) => {"ansible_loop_var": "item", "changed": false, "dest": "/tmp/[email protected]", "elapsed": 20, "gid": 0, "group": "root", "item": {"enable": false, "id": 3740, "name": "[email protected]", "url": "https://extensions.gnome.org/download-extension/compiz-alike-magic-lamp-effect@hermes83.github.com.shell-extension.zip?version_tag=34384"}, "mode": "0644", "msg": "Request failed: <urlopen error _ssl.c:980: The handshake operation timed out>", "owner": "root", "size": 21524, "state": "file", "uid": 0, "url": "https://extensions.gnome.org/download-extension/compiz-alike-magic-lamp-effect@hermes83.github.com.shell-extension.zip?version_tag=34384"}

Since it's impossible to specify retry and until when including a role, maybe this role could use some retries and until itself?

Thanks in advance