basic: fix ValueError if value of a type='int' is not an int

With this fix, we get a friendly error message:

    failed: [localhost] => {"failed": true}
    msg: value of argument start_port is not of type int and we were unable to automatically convert

lib/ansible/module_utils/basic.py

@@ -1016,6 +1016,7 @@ class AnsibleModule(object):
             value = self.params[k]
             is_invalid = False
 
+            try:
                 if wanted == 'str':
                     if not isinstance(value, basestring):
                         self.params[k] = str(value)
@@ -1067,6 +1068,8 @@ class AnsibleModule(object):
 
                 if is_invalid:
                     self.fail_json(msg="argument %s is of invalid type: %s, required: %s" % (k, type(value), wanted))
+            except ValueError, e:
+                self.fail_json(msg="value of argument %s is not of type %s and we were unable to automatically convert" % (k, wanted))
 
     def _set_defaults(self, pre=True):
         for (k,v) in self.argument_spec.iteritems():