Build params in command line

Ability to parse build parameters in the command line: $PARAM with
replaced with the value of build parameter PARAM. This is a quick fix,
there should be a more elegant way of doing this.
Fix builing the plugin in Jenkins' Buildhive environement

Fix taken from:
https://github.com/jenkinsci/testflight-plugin/commit/04b1ab8cc6d75cc634
e810dc72bacc50c518b09c
Added environement variables support and unit test

* Added environment variables support (and build variables) in and
elegant way using Jenkins Util class.
* Created Unit Test
* Fixed several warnings
* Changed identation to be GitHub-friendly
* Ignored Eclipse project files
Merge pull request #3 from butaca/master

Support parametrized command line arguments taken from build and environment variables (with build variables overriding environment variables).