BaseTools: Update python tool to call external tools with shell true mode

BaseTools: Update python tool to call external tools with shell true mode

Python tool may run from source as the dos batch files. So, update python
code to call external tools with shell true mode.

Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Erik Bjorge <erik.c.bjorge@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Erik Bjorge <erik.c.bjorge@intel.com>