Restrict client and socket example tests to K64F+K66F

I would like to restrict these to devices with "device_has": "EMAC", but
the framework doesn't currently permit that.  Revisit as more drivers
are EMAC-enabled or if the framework changes.

Author: kjbracey

tools/test/examples/examples.json

@@ -39,7 +39,7 @@
       ],
       "test-repo-source": "mbed",
       "features" : [],
-      "targets" : ["K64F", "NUCLEO_F429ZI"],
+      "targets" : ["K64F"],
       "toolchains" : ["GCC_ARM", "ARM"],
       "exporters": [],
       "compile" : true,
@@ -94,7 +94,7 @@
       ],
       "test-repo-source": "github",
       "features" : ["LWIP"],
-      "targets" : [],
+      "targets" : ["K64F", "K66F"],
       "toolchains" : [],
       "exporters": [],
       "compile" : false,
@@ -108,7 +108,7 @@
       ],
       "test-repo-source": "github",
       "features" : ["LWIP"],
-      "targets" : [],
+      "targets" : ["K64F", "K66F"],
       "toolchains" : [],
       "exporters": [],
       "compile" : true,