JayMessage uses the wrong user-agent when retrieving the WSDLs

### Expected result:
The user-agent of `ksoap2-android/2.6.0+;version=3.6.4` is used when Zeep retrieves the WSDLs.

### Actual result:
Zeep uses its own user-agent, `Zeep/4.0.0 (www.python-zeep.org)`.

### Impact:
No apparent impact, but this is unintended, and should be fixed for consistency.