Fix driver mode opt definition

Share driver mode opt should be StrOpt, but now it is ListOpt. We get driver
mode validation error when option is redefined within external config file.
It can not be caught by update of config opt within code.

Change-Id: I77cab322beba7ec2258e106eebf631c081cfebe5
Closes-Bug: #1403952
Merge "Fix driver mode opt definition"