Added possible json option value encoding

Sometimes mock has options that are python arrays, or dicts, before all the
options were used just as strings, now if possible, it will try to decode an
object using json parser.

Change-Id: I66feb645fab0308b7fea9e759cdb5d88b2278a41
Signed-off-by: David Caro <dcaroest@redhat.com>