LU-16521 tests: allow + separator for racer

LU-16521 tests: allow + separator for racer

The Test-Parameters: line parses ',' even with quotes, so it cannot
be used as a separator in Autotest for RACER_PROGS and RACER_EXTRA.

Allow both ',' and '+' as a separator for both RACER_PROGS and
RACER_EXTRA tasks so specific racer tasks can be run.

Do not always enable dir_remote and dir_migrate if RACER_PROGS set.

Test-Parameters: trivial testlist=racer env=RACER_PROGS=file_rename+file_truncate,RACER_EXTRA=file_create:5+dir_create:5+dir_remote:5
Fixes: 6d9e74580e ("LU-14274 tests: enhance racer to set extra layout")
Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
HPE-bug-id: LUS-11466
Change-Id: I3f3b4da6f76ccfac2680068184dc4714187a9a4d
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49866
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Deiter <alex.deiter@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>