Make this play nice in RHEL/CentOS Land

The package is `php-cli` in RedHat/RedHat-derivatives, not `php5-cli`. Let's catch the OS and account for that.
Merge pull request #5 from zamoose/patch-1

Make this play nice in RHEL/CentOS Land
Make the wp-cli install actually complete

This has to be set, otherwise wp-cli install routine ends up returning a `1` instead of a `0`, Puppet freaks out and thinks the install failed and so all downstream interactions that reply upon it being installed fail as a broken dependency.
Merge pull request #6 from zamoose/patch-2

Make the wp-cli install actually complete
Fix syntax error in wp::option
Add ability to set site URL
Change option name var to key

This is a backwards compatibility issue, but it wasn't working before, so
there's that.
Disambiguate wp::command's exec with location
fix for #9: $operatingsystem becomes $::operatingsystem
Merge pull request #12 from guaka/patch-1

$operatingsystem -> $::operatingsystem - Fixes #9
Add Puppet Forge module file

See #13
Add installation instructions
Ensure variables are interpolated correctly

Fixes #11
Download installer script from Github

I've been seeing intermittent issues where VIP Quickstart is having issues downloading the installer script from wp-cli.org. It seems to be fixed by downloading directly from Github instead. Additionally, we should probably re-download the installer each time. If there's an issue downloading it and a blank file gets created, it would be stuck with a blank installer forever unless you manually delete it.
Merge pull request #1 from joshbetz/patch-1

Use Github for WP-CLI installer source