[#437] removed dead code in install spec

was scaffolding for handling promises from the cordova cli
[#413] additional test for invalid platform argument
[#413] phonegap install has additional error checking to identify bad platform arguments and error out gracefully

two additional fail case tests in spec, test to see that the callback is executed with an error and nothing is thrown
[#439] one line fix, test set incorrect parameter to cause the function to fail (and therefore the test to pass)