Refactor pynag.Plugins.send_nsca into pynag.Utils

Patch does the following:
* Moves send_nsca into pynag.Utils
* Leave backwards compatible function in Plugins.simple
* New method is slightly more testable
* Fix mutable default argument
* Changed implementation to fix potential security vulnerability by
  allowing plugin output to escape shell string handling.
Added unit tests for Utils.send_nsca()
Plugins.simple.send_nsca - maintain backwards compatibility

Previously there was a typo where nscahost was spelt ncsahost in the argument list.

Now there is a backwards compatibility for that.
send_nsca() code cleanup
Merge pull request #118 from pynag/refactor-send_nsca

Refactor send nsca