ubuntu-cpc: avoid duplicate snaps listed in qcow manifest

commit a993592 introduced an additional call to create_manifest
(and snap-seed-parse) to write binary/boot/filesystem.packages. This
caused duplicate snap lines in the qcow manifest. This is because the
live-build/auto/binary code assumes that after 'lb binary' is run the
filesystem.packages will only have debs and it calls snap-seed-parse to
add them to the file. The commit changed filesystem.packages in the
ubuntu-cpc uefi binary hook to include debs and snaps.

This patch keeps the intent of the prior patch, updating the
filesystem.packages file for the content of the uefi disk image, but
only writes a listing of debian packages to match the expected content
of filesystem.packages.  The snaps will still be added in generic code
in live-build/auto/build.

debian/changelog

@@ -1,3 +1,9 @@
+livecd-rootfs (2.574ubuntu1) UNRELEASED; urgency=medium
+
+  * Remove duplicate snap listings in ubuntu-cpc qcow manifest
+
+ -- Robert C Jennings <robert.jennings@canonical.com>  Fri, 29 Mar 2019 15:39:13 -0500
+
 livecd-rootfs (2.574) disco; urgency=medium
 
   * Make serial-subiquity@ use the same codepath as tty1 subiquity.

live-build/ubuntu-cpc/hooks.d/base/disk-image-uefi.binary

@@ -93,11 +93,14 @@ install_grub() {
             ;;
     esac
 
-    # This call to generate the package manifest is added here to capture 
+    # This call to rewrite the debian package manifest is added here to capture
     # grub-efi packages that otherwise would not make it into the base
     # manifest. filesystem.packages is moved into place via symlinking to
     # livecd.ubuntu-cpc.manifest by live-build/auto/build after lb_binary runs
-    create_manifest "mountpoint" "binary/boot/filesystem.packages"
+    # and at that time snaps are added to the manifest (create-manifest is
+    # not called here as it calls snap-seed-parse, resulting in duplicate
+    # snap listings)
+    chroot mountpoint dpkg-query -W > binary/boot/filesystem.packages
 
     chroot mountpoint grub-install "${loop_device}" \
         --boot-directory=/boot \