finalize_bundle: Get sign key name of factory install shim

Some factory install shim are with file name like xxx_mp-v3.bin.
In the README, it will show sign key is "undefined" after finalize_bundle.
Modify regular expression to get sign key name.

TEST=manually finalize a bundle
     See correct sign key of install shim in the README file

Change-Id: I0796402f90dfb4fe9df881d4ea7d48f631ecd331
Commit-Queue: Bowgo Tsai <>
Tested-by: Bowgo Tsai <>
Reviewed-by: Justin Chuang <>
1 file changed