Update pxeboot-update script to accept parameter for
installer base URL
Add a common function to parse the port number from
inst.repo
Update pxeboot and kickstart URLs to support a configurable
HTTP port
Story: 2004642
Task: 28593
Depends-On: https://review.openstack.org/#/c/634237/
Change-Id: Ibd66e89e49794ca57b938eb43d227860eda6674a
Signed-off-by: Tao Liu <tao.liu@windriver.com>