More tests/coverage and bug fixes

[tejashah88]

• Added tests for fail cases and schemas/utterances
• Fixed bug while trying to retrieve schema/utterances with GET request
• Updated messages that display an error to be displayed by self.error
• Optimized some tests to not always start a new server instance after every test

[coveralls]

Changes Unknown when pulling 0ec22e4f3b1bb12f0e47e2ff7bc6a5a3cb892f03 on tejashah88:master into on alexa-js:master.

[dblock]

Lot of thumbs up from me! Merged.