Allow CasperJS URL to be overridden w/ env variable.
Allow CasperJS URL to be overridden w/ env variable.

This lets us default to dev domain on local machines, but use
alternative URLs for testing on QA, etc.

deadlybutter/phoenix,sergii-tkachenko/phoenix,DoSomething/dosomething,sbsmith86/dosomething,DoSomething/dosomething,jonuy/dosomething,mshmsh5000/dosomething,chloealee/dosomething,jonuy/dosomething,deadlybutter/phoenix,angaither/dosomething,jonuy/dosomething,sergii-tkachenko/phoenix,mshmsh5000/dosomething,deadlybutter/phoenix,sbsmith86/dosomething,chloealee/dosomething,angaither/dosomething,chloealee/dosomething,sbsmith86/dosomething,mshmsh5000/dosomething-1,DoSomething/phoenix,sbsmith86/dosomething,angaither/dosomething,mshmsh5000/dosomething,jonuy/dosomething,jonuy/dosomething,DoSomething/dosomething,deadlybutter/phoenix,chloealee/dosomething,chloealee/dosomething,DoSomething/phoenix,DoSomething/phoenix,sbsmith86/dosomething,chloealee/dosomething,angaither/dosomething,DoSomething/dosomething,angaither/dosomething,mshmsh5000/dosomething-1,DoSomething/phoenix,sbsmith86/dosomething,mshmsh5000/dosomething-1,deadlybutter/phoenix,mshmsh5000/dosomething-1,mshmsh5000/dosomething-1,DoSomething/dosomething,angaither/dosomething,mshmsh5000/dosomething,sergii-tkachenko/phoenix,DoSomething/dosomething,sergii-tkachenko/phoenix,jonuy/dosomething,DoSomething/phoenix,sergii-tkachenko/phoenix