NewDevice succeeds on non camera devices

[brucealthompson]

If I provide NewDevice() with an IPaddr and port that reference a web server, it will return success as long as the website hosted on that server does not return an http error. The issue is in "func (dev *Device) getSupportedServices(resp *http.Response)" This function does not check that the response is a valid SOAP response.

[brucealthompson]

I have been able to work around the issue stated above. Here are the problems I worked around:

1. onvif depends on "github.com/beevik/etree v1.3.0" but the go.mod file does not state this requirement. I updated my project to "github.com/beevik/etree v1.3.0" and now websites return an error to NewDevice()
2. if a site returns valid xml, NewDevice() returns success with a single service returned by device.GetServices(). I have had to add code to my application to catch this case.

It would be nice if you could fix the above issues even though I have worked around them.