Revert "Remove zeroing the disk, use fstrim+sync to trim the disk"

fstrim doesn't work at all in the image creation environment.

This reverts commit 8cad6efa4e.

fedora-cloud-base.ks

@@ -121,6 +121,18 @@ releasever=$(rpm --eval '%{fedora}')
 basearch=$(uname -i)
 rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-fedora-$releasever-$basearch
 
+echo "Zeroing out empty space."
+# Create zeros file with nodatacow and no compression
+touch /var/tmp/zeros
+chattr +C /var/tmp/zeros
+# This forces the filesystem to reclaim space from deleted files
+dd bs=1M if=/dev/zero of=/var/tmp/zeros || :
+echo "(Don't worry -- that out-of-space error was expected.)"
+# Force sync to disk (Cf. https://pagure.io/cloud-sig/issue/340#comment-743430)
+btrfs filesystem sync /
+rm -f /var/tmp/zeros
+btrfs filesystem sync /
+
 # When we build the image a networking config file gets left behind.
 # Let's clean it up.
 echo "Cleanup leftover networking configuration"
@@ -129,12 +141,8 @@ rm -f /etc/NetworkManager/system-connections/*.nmconnection
 # Clear machine-id on pre generated images
 truncate -s 0 /etc/machine-id
 
-# Use fstrim to trim the disk of unused blocks
-# Cf. BZ#1971186
-echo "Trimming the disk of unused blocks."
+# add fstrim -av to the post section until BZ#1971186 is resolved
 fstrim -av
-# Force sync to disk (Cf. https://pagure.io/cloud-sig/issue/340#comment-743430)
-btrfs filesystem sync /
 
 %end
 ##### end kickstart post ############################################