Add -E flag to chef-solo in order to enable people use the new environment support in chef-solo.

http://tickets.opscode.com/browse/CHEF-3356 has added environment support to chef-solo. However using chef-solor from command line users can not make use of this because they can't set the environment for the node in chef-solo. 

This PR add -E flag support to chef-solo therefore people can set the environment if they want to make use of it. 

I've tested env_run_lists via roles and environment attributes manually and looking good with -E flag.