Update certificates for OpenFlow TLS connection

Update certificates for OpenFlow TLS connection

Certificate chains with intermediate CAs, currently used for
the OpenFlow channel TLS connection for testing, is not supported
by Open vSwitch.

Replace certificates/keystores for the switch & controller with
the ones signed directly by the root CA and create a new script,
gen-certs.sh, to make it easier to generate new certificates.

Also, fix an error in MininetKeywords in executing 'ovs-vsctl get-ssl'
command.

Signed-off-by: Sangwook Ha <sangwook.ha@verizon.com>
Change-Id: Ieb0c3c4f8285336a4ed4b48412c5d0e2fc7b27cb