build: make scripts in gyp run with right python

Author: gengjiawen

node.gyp

@@ -429,7 +429,7 @@
                'inputs': [ '<(opensslconfig)', ],
                'outputs': [ '<(opensslconfig_internal)', ],
                'action': [
-                 'python', 'tools/copyfile.py',
+                 '<(python)', 'tools/copyfile.py',
                  '<(opensslconfig)',
                  '<(opensslconfig_internal)',
                ],

tools/v8_gypfiles/v8.gyp

@@ -1772,7 +1772,7 @@
             }],
           ],
           'action': [
-            'python', '<(V8_ROOT)/tools/testrunner/utils/dump_build_config_gyp.py',
+            '<(python)', '<(V8_ROOT)/tools/testrunner/utils/dump_build_config_gyp.py',
             '<@(v8_dump_build_config_args)',
           ],
         },
@@ -1866,7 +1866,7 @@
             '<(SHARED_INTERMEDIATE_DIR)/debug-support.cc',
           ],
           'action': [
-            'python',
+            '<(python)',
             '<(V8_ROOT)/tools/gen-postmortem-metadata.py',
             '<@(_outputs)',
             '<@(heapobject_files)'