oci: use .list format for source.list.d entry

Use .list format instead of .sources. This will allow for better
compatibility with the version from our APT repositories.

Change-Id: I18e1cca6fb9e0e6fa6fa62add0868ea133a37b29

packaging/rules/debian-one-click-install/ring-all.postinst

@@ -73,7 +73,7 @@ HUFCGSHO3/kzxSlkE1PBUX3IZ8PSFijyopBnWUhlSXuyRjte8OR7Fl/Rlf0IaOD1
 # In general: you will not need to modify these variables.
 # WARNING: When modifying the paths, keep in mind that the corresponding
 # postrm paths should be modified as well
-APT_FILE="/etc/apt/sources.list.d/ring-main.sources"
+APT_FILE="/etc/apt/sources.list.d/ring-main.list"
 UPDATE_MANAGER_PATH="/etc/update-manager/release-upgrades.d/"
 RING_UPDATE_MANAGER_ID="ring-main"
 
@@ -131,15 +131,7 @@ EOF
             # Add an entry for the package repository to the trusted package
             # sources (DEB822 format)
             cat > $APT_FILE <<EOF
-# This file makes sure that Ring is kept up-to-date
-# as part of regular system upgrades
-
-Types: deb
-URIs: $RING_REPO
-Suites: ring
-Architectures: i386 amd64
-Components: main
-Signed-By: $RING_KEY_FINGERPRINT
+deb ${RING_REPO} ring main
 EOF
 
             # Additionally, if update manager is installed we inform it about