[webapi][XWALK-2312] Fixed vconftool permission for geoallow

- vconftool command need root permission, so excute this command as pre-condition

Impacted TCs num(approved): New 0, Update 0, Delete 0
Unit test Platform: Tizen IVI
Tizen test result summary: Pass 99, Fail 105, Blocked 7
TBD is not acceptable