For anyone having problems with sudo on cloud servers: the netinstall script will overwrite the file /etc/sudoers with a custom one. This is fine for standalone servers, but it is conflictive with cloud instances where that file already exists with custom cloud setups. The solution is to find the original /etc/sudoers file for your cloud server, and restore it back.
Then create a new file /etc/sudoers.d/issabel with this content
asterisk ALL = NOPASSWD: /sbin/shutdown
asterisk ALL = NOPASSWD: /sbin/service
asterisk ALL = NOPASSWD: /sbin/chkconfig
asterisk ALL = NOPASSWD: /usr/sbin/issabel-helper
We fixed this for the next Issabel release, due out shortly.