BaseTools: Remove equality operator with None

replace "== None" with "is None" and "!= None" with "is not None"

Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>

BaseTools/Source/Python/Common/EdkIIWorkspace.py

@@ -38,7 +38,7 @@ class EdkIIWorkspace:
         #
         # Check environment valiable 'WORKSPACE'
         #
-        if os.environ.get('WORKSPACE') == None:
+        if os.environ.get('WORKSPACE') is None:
             print 'ERROR: WORKSPACE not defined.    Please run EdkSetup from the EDK II install directory.'
             return False