PciAssignable: Make nic_name_re configurable.

nic_name_re used to filter nic name in host.

Signed-off-by: Feng Yang <fyang@redhat.com>
PciAssignable: Do not modprobe it, if self.driver is not available.

Signed-off-by: Feng Yang <fyang@redhat.com>
Merge pull request #1722 from FengYang/PciAssignable

Two update for PciAssignable class