Switch Node back to using libuv iomgr by default

binding.gyp

@@ -39,11 +39,9 @@
 {
   'variables': {
     'runtime%': 'node',
-    # UV integration in C core is disabled by default while bugs are ironed
-    # out. It can be re-enabled for one build by setting the npm config
-    # variable grpc_uv to true, and it can be re-enabled permanently by
-    # setting it to true here.
-    'grpc_uv%': 'false',
+    # UV integration in C core is enabled by default. It can be disabled
+    # by setting this argument to anything else.
+    'grpc_uv%': 'true',
     # Some Node installations use the system installation of OpenSSL, and on
     # some systems, the system OpenSSL still does not have ALPN support. This
     # will let users recompile gRPC to work without ALPN.

templates/binding.gyp.template

@@ -41,11 +41,9 @@
   {
     'variables': {
       'runtime%': 'node',
-      # UV integration in C core is disabled by default while bugs are ironed
-      # out. It can be re-enabled for one build by setting the npm config
-      # variable grpc_uv to true, and it can be re-enabled permanently by
-      # setting it to true here.
-      'grpc_uv%': 'false',
+      # UV integration in C core is enabled by default. It can be disabled
+      # by setting this argument to anything else.
+      'grpc_uv%': 'true',
       # Some Node installations use the system installation of OpenSSL, and on
       # some systems, the system OpenSSL still does not have ALPN support. This
       # will let users recompile gRPC to work without ALPN.