Add network namespace support

RedHat kernels do not have network namespaces
enabled by default. This patch uses the netns class
in openstacklib to check if network namespaces are
available, and if they are not, install the latest kernel.

Ubuntu hosts are unaffected, and should contain netns support
in all common cases anyway.

Change-Id: Ided02a7bfe57ab3e318c7ac24df0eeb54b349c08
Merge "Add network namespace support"