LU-14875 import: fix bad CPT read

LU-14875 import: fix bad CPT read

When importing, CPT was read from tunables field but in fact, it is in
the same level in the YAML file generated during export.

Test-parameters: trivial testlist=sanity-lnet

Signed-off-by: Cyril Bordage <cbordage@whamcloud.com>
Change-Id: Iea7b6189ad1a25b95ae6416d75ee2cbe4dca2fbf
Reviewed-on: https://review.whamcloud.com/46541
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>