Execute a shell command remotely and return the output.

        Simplified version of Popen when you only want the output as a string and detect any errors.

def check_output(self, cmd):
        """
        Execute a shell command remotely and return the output.

        Simplified version of Popen when you only want the output as a string and detect any errors.
        """
        p = self.Popen(cmd, stdout=subprocess.PIPE)
        output, _ = p.communicate()
        if p.returncode != 0:
            raise RemoteCalledProcessError(p.returncode, cmd, self.host, output=output)
        return output