Fedora/CentOS specific fixes in devstack engine

Got following issues with Fedora and CentOS:

 * only tcp port 22 is open by default
 * requiretty is true in sudoers
 * no /sbin in $PATH

Change-Id: I7467864059512c1aee2645c0cba46a80db7a055b
Merge "Fedora/CentOS specific fixes in devstack engine"