Run hooks on 'deploy' only and fix tests

Mina hooks were running on every invocation of `mina`. Now mina-hooks
checks for the deploy argument and will only run when deploying.

Tests:
* Update tests for the mina scope that weren't running. Create a Rake
  task environment that simulates the env created when Rake loads
  a rake file so mina and mina-hooks are available. Move assertions
  outside the block to correctly access the mina app scope.

* Update test helpers to create random task names and expose more of
  the internal scope for testing.
Update Changelog
Release version 0.2