REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2101
This patch is going to remove unnecessary calls
of os.exist()
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>