LU-10893 tests: allow to disable dm-flakey layer

LU-10893 tests: allow to disable dm-flakey layer

The patch 54b9e3f789358bd9dfb94b77fe33a4faa1e28ab2 adds flakey layer
to test framework. But it also adds a regression, you can`t run tests
separately from a setup. Before the dm-flakey, it was easy to create a
configuration at ncli, setup a cluster, and start a test. But now it
is impossible. For example
sudo MDSDEV=/dev/sdb MDSDEV1=/dev/sdb sh lustre/tests/llmount.sh
sudo MDSDEV=/dev/sdb MDSDEV1=/dev/sdb ONLY=0 sh
lustre/tests/conf-sanity.sh
	Format mds1: /dev/sdb
	mkfs.lustre FATAL: Unable to build fs /dev/sdb (256)
	mkfs.lustre FATAL: mkfs failed 256

The fix disables dm-flakey layer with option FLAKEY=false.

Test-Parameters: envdefinitions=FLAKEY=false
Signed-off-by: Alexander Boyko <c17825@cray.com>
Cray-bug-id: LUS-5851
Change-Id: I248be2307cff5fe6b4b2524478ca8e4cd96a77d2
Reviewed-on: https://review.whamcloud.com/32658
Reviewed-by: Elena Gryaznova <c17455@cray.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Jenkins
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>