change for centos "ip link set master" to "brctl"
if ip link set is failed, then try brctl addif.
Merge remote-tracking branch 'upstream/master' into for-centos

Conflicts:
	pipework
rebase master
Merge pull request #14 from WhiteAnthrax/for-centos

Fallback on brctl if "ip … set master" fails (for CentOS).