zdtm: Make possible to claim for features list

Currently, one feature is supported. Add possibility
for a test to depend on several features.

v2: Delete excess "if" as suggested by Andrey Vagin.
    Rename variables to decrise patch size.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>