udev: prevent race with kpartx -d

udevd calls (internal) blkid, which opens the device, so kpartx -d
cannot remove it.

system-config/00-qubes-ignore-devices.rules

@@ -2,5 +2,9 @@
 
 ACTION!="remove", SUBSYSTEM=="block", KERNEL=="loop*", ENV{DM_UDEV_DISABLE_DISK_RULES_FLAG}="1"
 # ENV{DM_NAME} not available yet
+# Template VM disks
 ACTION!="remove", SUBSYSTEM=="block", ATTR{dm/name}=="snapshot-*", ENV{DM_UDEV_DISABLE_DISK_RULES_FLAG}="1"
 ACTION!="remove", SUBSYSTEM=="block", ATTR{dm/name}=="origin-*", ENV{DM_UDEV_DISABLE_DISK_RULES_FLAG}="1"
+# kpartx used for creating empty volatile.img, udevd tries to access the device
+# and prevent kpartx from removing them
+ACTION!="remove", SUBSYSTEM=="block", ATTR{dm/name}=="loop*p*", ENV{DM_UDEV_DISABLE_DISK_RULES_FLAG}="1"