Ignore bridge template names with multiple printf conversions

Ignore bridge template names with multiple printf conversions

For some reason, we allow a bridge name with %d in it, which we replace
with an unsigned integer to form a bridge name that does not yet exist
on the host.

Do not blindly pass it to virAsprintf if it's not the only conversion,
to prevent crashing on input like:

<network>
  <name>test</name>
  <forward mode='none'/>
  <bridge name='virbr%d%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s'/>
</network>

Ignore any template strings that do not have exactly one %d conversion,
like we do in various drivers before calling virNetDevTapCreateInBridgePort.