cobertura plugin, adding support for multi config projects

[timothy.f...@seagate.com]

Hello Devs,

There seems to be a significant amount of interest around adding support for coberturas code coverage using multi config projects.

https://github.com/jenkinsci/cobertura-plugin/pull/53

https://github.com/jenkinsci/cobertura-plugin/pull/26

53 is mine, I took 26 and added passing env vars through the plugin. 

I think we should get this merged. We have been using this 53 successfully for awhile now. 

Thanks!