when build.py was failing to build packages but was not providing any
error message except for “Failed to start command.” this patch provide
the error message.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>