Spice events have mostly similar information present in the event JSON
but they differ in the name of the element containing the port.

The JSON event also provides connection ID which might be useful in the
future.

This patch splits up the event parser code into two functions and the
SPICE reimplements the event parsing with correct names and drops the
VNC only stuff.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1236585