Comment 6 for bug 1673350

Error logs:
----------

This error log is seen in the installer, and multipath devices are not
created for such storage system:

...
Mar 14 06:41:54 kernel: [ 0.000000] Kernel command line: tasks=standard pkgsel/language-pack-patterns= pkgsel/install-language-support=false --- quiet /install disk-detect/multipath/enable=true
...
Mar 14 06:47:09 main-menu[3743]: INFO: Menu item 'disk-detect' selected
...
Mar 14 06:47:14 anna-install: Installing multipath-udeb
...
Mar 14 06:47:16 kernel: [ 324.968027] device-mapper: table: 252:0: multipath: unknown path selector type
Mar 14 06:47:16 kernel: [ 324.968030] device-mapper: ioctl: error adding target to table
...
Mar 14 06:47:17 kernel: [ 326.484059] device-mapper: table: 252:0: multipath: unknown path selector type
Mar 14 06:47:17 kernel: [ 326.484062] device-mapper: ioctl: error adding target to table
Mar 14 06:47:17 disk-detect: Mar 14 06:47:16 | mpatha: ignoring map
...
Mar 14 06:47:17 disk-detect: Mar 14 06:47:17 | mpathg: ignoring map
Mar 14 06:47:18 disk-detect: No multipath devices detected

And after installing the system in an individual/single path device,
and trying to switch to multipath via multipath-tools-boot, it also
happens in the initramfs:

Begin: Mounting root file system ... Begin: Running /scripts/local-top ... done.
Begin: Running /scripts/local-premount ... Begin: Waiting for udev to settle (multipath) ... done.
[ 89.709480] device-mapper: table: 252:0: multipath: unknown path selector type
[ 89.709537] device-mapper: ioctl: error adding target to table
[ 89.756251] device-mapper: table: 252:0: multipath: unknown path selector type
[ 89.837132] device-mapper: ioctl: error adding target to table
[ 89.912346] device-mapper: table: 252:0: multipath: unknown path selector type
[ 90.001719] device-mapper: ioctl: error adding target to table
[ 90.300203] device-mapper: table: 252:0: multipath: unknown path selector type
[ 90.303521] device-mapper: ioctl: error adding target to table
Begin: Running /scripts/local-block ... done.
Begin: Running /scripts/local-block ... done.
Begin: Running /scripts/local-block ... done.
...
Begin: Running /scripts/local-block ... done.
done.

Gave up waiting for root device. Common problems:
 - Boot args (cat /proc/cmdline)
   - Check rootdelay= (did the system wait long enough?)
   - Check root= (did the system wait for the right device?)
 - Missing modules (cat /proc/modules; ls /dev)
ALERT! UUID=0568fc48-2921-4ba2-b1b5-127c1d5a310e does not exist. Dropping to a shell!

BusyBox v1.22.1 (Ubuntu 1:1.22.0-15ubuntu1) built-in shell (ash)
Enter 'help' for a list of built-in commands.

(initramfs)