add listener port and ip option for 'pleroma.instance gen' and enable its test
Issue: #1070 (closed)
Another thing fixed in this MR is test file test/tasks/instance.exs
was named incorrectly, so it was never running.
This has been fixed by renaming it.
test/tasks/instance.exs -> test/tasks/instance_test.exs
Edited by Sachin Joshi