BaseTools ConvertMasmToNasm: Support Python 3
BaseTools ConvertMasmToNasm: Support Python 3

The script is updated to support both python 2.7 and python 3.

v2:
 * Use io.open() rather than open() (Jaben)

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <a79006884ba9cf5f4f7fcbb92a15b208780d8c97@intel.com>
Cc: Yonghong Zhu <78d981fe33a016071af5222c56d5cf77f30fb0b2@intel.com>
Cc: Liming Gao <6480311aeeb4b006862f6d13ebabddc03f51e507@intel.com>
Cc: Erik Bjorge <330ad10f99fcdfb914fa4e3b5d9f2ec8c03e31ae@intel.com>
Reviewed-by: Liming Gao <6480311aeeb4b006862f6d13ebabddc03f51e507@intel.com>
Reviewed-by: Erik Bjorge <330ad10f99fcdfb914fa4e3b5d9f2ec8c03e31ae@intel.com>

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