module/boot@/configure/configure: fix a test for ZFS_IMPORT.

See merge request obmods/boot-66serv!3

system-fsck: replace s6-test with test.

See merge request obmods/boot-66serv!2

s6-test was moved to execline and eltest, deprecated from s6-portable-
utils and finally removed in v. 2.3.0.0. The service will fail with
exit code 111 and the boot will hang without replacing it.

Add checks to the configure script and improve devices-* services.

See merge request obmods/boot-66serv!1

in the environment/configuration file.
Also change the devices naming.

the opportunity to actually see the warnings.

Also fix language on system-Devices and devices-mdraid.

swapon does not fail when there is no swap partition/file, so it makes
sense to have a stricter test.

- use disks/devices/filesystems/volume groups consistently
- naming is based on the output of the relevant commands and/or the
manpages

- remove check_empty_var() and replace with check_var_existance() for
FIREWALL
- add a check for the ZFS_IMPORT values

in the [environment]

- add devices-mdraid frontend service file
- add devices-mdraid in the @depends array of devices-crypttab,
devices-lvm and in the @contents array of system-devices.

- make the check for the utility not fatal - exist with a warning
- make the dmraid invocation more verbose (it not easy to add the same
check as in other services)
- make the crash message a warning.