encode strings to utf-8 in ServiceInfo

I found that properties dict values registered as "False" rather than the intended string value, such as "path" in the provided examples.

eg.

Service Paul's Test Web Site._http._tcp.local. added
  Type is _http._tcp.local.
  Address is 10.0.1.2:80
  Weight is 0, Priority is 0
  Server is ash-2.local.
  Properties are
    path: False