LU-16804 tests: load CONFIG at beginning of init_test_env

LU-16804 tests: load CONFIG at beginning of init_test_env

In order to have all environment variables properly loaded, make
CONFIG loaded at the beginning of init_test_env().

Lustre-change: https://review.whamcloud.com/50914
Lustre-commit: fdbb2bc8495064e1d9e61f02bcfd13b1e6aec8da

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I1c3caa3d582c4b317ff3d0d10fc0103e046ddf17
Reviewed-by: Sarah Liu <sarah@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53250
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>