Log CombinedOutput instead of just Output

[maddie]

Output() only shows the messages written to stdout but not stderr. Switching to CombinedOutput() would log both stdout and stderr to result.Error.CmdOutput.

[coveralls]

Coverage increased (+1.6%) to 96.774% when pulling 13ada9c849314ba5fdb68cbf958342c0a5175fb2 on maddie:master into 40c7487d7d9c82ffe0bb4f89ced3813abd20e439 on keighl:master.