Allow to provide customized DispVM home directly in the template VM

This significantly speeds up DispVM creation for large customized
homes, since no data has to be copied, and instead CoW is used.

misc/dispvm-prerun.sh

@@ -3,10 +3,12 @@
 apps="/usr/libexec/evinced"
 
 #If user have customized DispVM settings, use its home instead of default dotfiles
-if [ -e /rw/home/user/.qubes-dispvm-customized ]; then
-	cp -af /rw/home/user /home/
-else
-	cat /etc/dispvm-dotfiles.tbz | tar -xjf- --overwrite -C /home/user --owner user 2>&1 >/tmp/dispvm-dotfiles-errors.log
+if [ ! -e /home/user/.qubes-dispvm-customized ]; then
+	if [ -e /rw/home/user/.qubes-dispvm-customized ]; then
+		cp -af /rw/home/user /home/
+	else
+		cat /etc/dispvm-dotfiles.tbz | tar -xjf- --overwrite -C /home/user --owner user 2>&1 >/tmp/dispvm-dotfiles-errors.log
+	fi
 fi
 
 for app in $apps ; do

vm-systemd/mount-dirs.sh

@@ -79,10 +79,12 @@ if [ -e /var/run/qubes-service/qubes-dvm ]; then
     touch /etc/this-is-dvm
 
     #If user have customized DispVM settings, use its home instead of default dotfiles
-    if [ -e /rw/home/user/.qubes-dispvm-customized ]; then
-        cp -af /rw/home/user /home/
-    else
-        cat /etc/dispvm-dotfiles.tbz | tar -xjf- --overwrite -C /home/user --owner user 2>&1 >/tmp/dispvm-dotfiles-errors.log
+    if [ ! -e /home/user/.qubes-dispvm-customized ]; then
+        if [ -e /rw/home/user/.qubes-dispvm-customized ]; then
+            cp -af /rw/home/user /home/
+        else
+            cat /etc/dispvm-dotfiles.tbz | tar -xjf- --overwrite -C /home/user --owner user 2>&1 >/tmp/dispvm-dotfiles-errors.log
+        fi
     fi
 else
     mount /home