Use per-test-unique host names

Avoids race conditions with immediately re-used LVs.

examples/release-testing

@@ -1,9 +1,6 @@
 #!/bin/sh
 
 # Skip dapper and edgy due to bug #659360 in debootstrap
-for dist in $(awk '!/^#|^$/ {print $1}' /etc/xen-tools/distributions.conf | egrep -v '^(dapper|edgy)$'); do
-    xen-create-image --dist $dist --force --verbose "$@" || break
-    # Work around umount being sometimes too slow
-    sync
-    sleep 5
+for dist in $(awk '!/^#|^$/ {print $1}' /etc/xen-tools/distributions.conf | egrep -v '^(dapper|edgy|buster|bullseye)$'); do
+    xen-create-image --dist $dist --hostname "xen-tools-release-testing-$dist" --force --verbose "$@" || break
 done 2>&1 | tee xen-tools-release-testing.log