Pkcs7Sign, Rsa2048Sha256Sign and Rsa2048Sha256GenerateKeys doesn't work on Linux. It needs to be changed with shell=True. Fixes: https://bugzilla.tianocore.org/show_bug.cgi?id=423 Cc: Liming Gao <liming.gao@intel.com> Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com> Reviewed-by: Liming Gao <liming.gao@intel.com>