Prevent uninitialized variable in factory_WriteGBB

In order to prevent running the write GBB test without
proper pre-requisition, test and provide error messages
when the component file pattern cannot be found.

BUG=chrome-os-partner:969
TEST=manually test with command line, should give error messages
without unhandled exception.

Change-Id: Ib3ae4261dccc78e61e76967c3fcd6ef21f8e079f

Review URL: http://codereview.chromium.org/3473008
1 file changed