conf: extra validation for <port isolated='yes'/>

conf: extra validation for <port isolated='yes'/>

During the hypervisor-agnostic validation of network devices, verify
that the interface type is either "network" or "bridge", and that if
there is any <virtualport>, that it doesn't have any type associated
with it.

This needs to be done both for the parse-time validation and for
runtime validation (after a port has been acquired from any associated
network), because an interface with type='network' could have an
actual type at runtime of "hostdev" or "direct", neither of which
support isolated='true' (yet). Likewise, if an interface is
type='network', then at runtime a <virtualport> with a type that
doesn't support isolated='yes' (e.g. "openvswitch", "802.1Qbh" -
currently *none* of the available virtualport types support it)

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>