ros config merge broken from stdin on v1.5.1

[riaan53]

RancherOS Version: (ros os version)
ros v1.5.1

Where are you running RancherOS? (docker-machine, AWS, GCE, baremetal, etc.)
virtualbox

On ros v1.5.0 I can pipe in ros config like this:

cat somefile.yaml | ros config merge

But on ros v1.5.1 I get the following error for the exact same command:

FATAL input parameter cannot be empty

It still works when loading the file via the -i argument but we are doing it programatically and writing a file first is not ideal.

[niusmallnan]

@kingsd041 Please add this function to our validation tests.

[rootwuj]

Tested with rancher/os:v1.5.2-rc1 from May 17
This version supports the ros config merge command.
Verified fixed