mock's return value for processutils.ssh_execute
mock's return value for processutils.ssh_execute

In tests/drivers/test_ssh.py, SSHPrivateMethodsTestCase tests are mocking
processutils.ssh_execute() and sets its return value to a list. However,
processutils.ssh_execute() doesn't return a list, it returns a tuple: (stdout, stderr).

This fixes the tests, by changing the return values to (stdout, stderr) tuples.

Change-Id: If146d80ad9acd33bd5c676e6b2ba2142c9b07a84
Closes-Bug: #1273452

naterh/ironic,ramineni/myironic,varunarya10/ironic,bacaldwell/ironic,ionutbalutoiu/ironic,redhat-openstack/ironic,openstack/ironic,pshchelo/ironic,rdo-management/ironic,pshchelo/ironic,NaohiroTamura/ironic,Tan0/ironic,supermari0/ironic,dims/ironic,SauloAislan/ironic,openstack/ironic,rackerlabs/ironic,dims/ironic,bacaldwell/ironic,NaohiroTamura/ironic,naototty/vagrant-lxc-ironic,ionutbalutoiu/ironic,SauloAislan/ironic,naototty/vagrant-lxc-ironic,JioCloud/ironic,faizan-barmawer/openstack_ironic,froyobin/ironic,debayanray/ironic_backup,devananda/ironic,hpproliant/ironic,Tehsmash/ironic