Updating information for building AGL cluster images

Updating Run aglsetup.sh scripts
Updating Using BitBake image information

Bug-AGL: [SPEC-4604]
Signed-off-by: Vinod Ahuja <vahuja@unomaha.edu>
Change-Id: If6489d14c0e479b6fa10ee4c97863aae4829abe2
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/documentation/+/28637
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
(cherry picked from commit 7b4f6a32f8e6f2389a039e19462e70ca30ed4196)
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/documentation/+/28614