Couple of fixes to make this playbook work more reliably.

* Add second apt-get update to snipeit.sh prior to apt-get. This resolves an issue if repo URLS are stale.
* Require ``Curl`` command in playbook. Needed to install composer.
* Modify a few paths to use forward slashes instead of a back slash.
* Add install requirements for Vagrant. Should help users with ``fresh`` boxes. Ansible is a requirement on the Mac Client for Vagrant to work.

Since I didn't add this in my first commits...Thank you!!! This has been super helpful.