Edit Open vSwitch license info so that GitHub recognizes it.

Edit Open vSwitch license info so that GitHub recognizes it.

GitHub uses a library called Licensee to identify a project's license
type. It shows this information in the status bar and via the API if it
can unambiguously identify the license.

This commit creates a LICENSE file that stores the full text of the
Apache license. It also removes the COPYING file and transfers its
contents to a new "License" section in the README.

Collectively, these changes allow Licensee to successfully identify the
license type of Open vSwitch's codebase as Apache.

Submitted-at: https://github.com/openvswitch/ovs/pull/224
Signed-off-by: Andrea Kao <eirinikos@gmail.com>
[blp@ovn.org removed references to COPYING and updated Makefile.am]
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Aaron Conole <aconole@redhat.com>