reproducible: only use disorderfs if it's available

hosts/jenkins/etc/pbuilder/rebuild-hooks/B01_cleanup

@@ -6,5 +6,7 @@ set -e
 [ "$(readlink /proc/1/ns/uts)" = "$(readlink /proc/self/ns/uts)" ] && exit 0
 
 # cease using disorderfs
-sudo -u pbuilder2 fusermount -u /tmp/buildd
-mv /tmp/disorderfs /tmp/buildd
+if [ -d /tmp/disorderfs ] ; then
+	sudo -u pbuilder2 fusermount -u /tmp/buildd
+	mv /tmp/disorderfs /tmp/buildd
+fi

hosts/jenkins/etc/pbuilder/rebuild-hooks/C01_cleanup

@@ -6,5 +6,7 @@ set -e
 [ "$(readlink /proc/1/ns/uts)" = "$(readlink /proc/self/ns/uts)" ] && exit 0
 
 # cease using disorderfs
-sudo -u pbuilder2 fusermount -u /tmp/buildd
-mv /tmp/disorderfs /tmp/buildd
+if [ -d /tmp/disorderfs ] ; then
+	sudo -u pbuilder2 fusermount -u /tmp/buildd
+	mv /tmp/disorderfs /tmp/buildd
+fi

hosts/jenkins/etc/pbuilder/rebuild-hooks/D01_modify_environment

@@ -13,5 +13,9 @@ echo "I: Adding a custom variable just for the fun of it..." >&2
 export CAPTURE_ENVIRONMENT="I capture the environment"
 
 # use disorderfs, mount it as user
-mv /tmp/buildd /tmp/disorderfs
-sudo -u pbuilder2 disorderfs /tmp/disorderfs /tmp/buildd
+if [ -x /usr/bin/disorderfs ] ; then
+	mv /tmp/buildd /tmp/disorderfs
+	sudo -u pbuilder2 disorderfs /tmp/disorderfs /tmp/buildd
+else
+	echo "Warning: disorderfs not available."
+fi