I started fresh copy of the WSO2 API Manager 1.8 and get below error for no reason.
ERROR - ListenerManager Couldn\'t initialize the httpstransport listener
Check the system hostname by running following command
$ hostname
try to ping to the output for that hostname.
$ ping
If that gives an error check the /etc/hosts file. At least it should have a host entry to 127.0.0.1
/etc/hosts
127.0.0.1 or