Switches to use the IPA builder project for building IPA images.

Switches the IPA images used by default to CentOS 8 based image.

Changes the file extension of the IPA kernel image from vmlinuz to
kernel.

Story: 2007070
Task: 37953

Change-Id: I82fc455f41f48dacb453e135870dd776895d7c99
Story: 2006574
Task: 39485