Reduce the runtime of the GELI tests

There is no reduction in test coverage. On my system runtime is reduced
from 38m32s to 6m24s.

tests/sys/geom/class/eli/conf.sh
tests/sys/geom/class/eli/init_a_test.sh
tests/sys/geom/class/eli/init_test.sh
tests/sys/geom/class/eli/integrity_copy_test.sh
tests/sys/geom/class/eli/integrity_data_test.sh
tests/sys/geom/class/eli/integrity_hmac_test.sh
tests/sys/geom/class/eli/onetime_a_test.sh
tests/sys/geom/class/eli/onetime_test.sh
Move the looping code into common functions in conf.sh, and remove
alias ciphers from the list.

tests/sys/geom/class/eli/init_a_test.sh
tests/sys/geom/class/eli/init_test.sh
tests/sys/geom/class/eli/integrity_copy_test.sh
tests/sys/geom/class/eli/integrity_data_test.sh
tests/sys/geom/class/eli/integrity_hmac_test.sh
tests/sys/geom/class/eli/onetime_a_test.sh
Move a few commands that don't need to be in the inner loop out.

tests/sys/geom/class/eli/init_test.sh
tests/sys/geom/class/eli/onetime_a_test.sh
Reduce the sector count

tests/sys/geom/class/eli/Makefile
tests/sys/geom/class/eli/init_alias_test.sh
Add a test for initializing a GELI device using one of the cipher
aliases, and check that the alias is correctly interpreted.

MFC after: 4 weeks
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D8814