Remove config_path setting and amend regex in mbed config JSON schema

- Removed the config_path setting from schema and moved the addition of the
config_path value after the validation is done.

- Altered the macro validation regex to be more lenient. Now verifies that
  if '=' is used in the macro definition that something comes after it.

tools/config/__init__.py

@@ -465,8 +465,6 @@ class Config(object):
                 sys.stderr.write(str(exc) + "\n")
                 continue
 
-            cfg["__config_path"] = full_path
-
             # Validate the format of the JSON file based on the schema_lib.json
             schema_path = os.path.join(os.path.dirname(__file__),
                                        "schema_lib.json")
@@ -477,6 +475,8 @@ class Config(object):
             if errors:
                 raise ConfigException(",".join(x.message for x in errors))
 
+            cfg["__config_path"] = full_path
+
             # If there's already a configuration for a module with the same
             # name, exit with error
             if self.lib_config_data.has_key(cfg["name"]):

tools/config/schema_app.json

@@ -95,13 +95,9 @@
       "type": "array",
       "items": {
         "type": "string",
-        "pattern": "^([A-Za-z0-9_]+|[A-Za-z0-9_]+=[0-9]+|[A-Za-z0-9_]+=\\\".*\\\")$"
+        "pattern": "(^[\\w]+$|^[\\w]+=.+$)"
       }
     },
-    "__config_path": {
-      "description": "Path to configuration file",
-      "type": "string"
-    },
     "artifact_name": {
       "type": "string"
     }

tools/config/schema_lib.json

@@ -95,12 +95,8 @@
       "type": "array",
       "items": {
         "type": "string",
-        "pattern": "^([A-Za-z0-9_]+|[A-Za-z0-9_]+=[0-9]+|[A-Za-z0-9_]+=\\\".*\\\")$"
+        "pattern": "(^[\\w]+$|^[\\w]+=.+$)"
       }
-    },
-    "__config_path": {
-      "description": "Path to configuration file",
-      "type": "string"
     }
   },
   "required": [