qemu/conf: set HOTPLUGGABLE connect flag during PCI address set init

qemu/conf: set HOTPLUGGABLE connect flag during PCI address set init

virDomainPCIAddressBusSetModel() is called for each PCI controller
when building an address set prior to assiging PCI addresses to
devices.

This patch adds a new argument, allowHotplug, to that function that
can be set to false if we know for certain that a particular
controller won't support hotplug

The most interesting case is in qemuDomainPCIAddressSetCreate(), where
the config of each existing controller is available while building the
address set, so we can appropriately set allowHotplug = false when the
user has "hotplug='off'" in the config of a controller that normally
would support hotplug. In all other cases, it is set to true or false
in accordance with the capability of the controller model.

So far we aren't doing anything with this bus flag in the address set.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>