Added openvpn patterns

[jespereneberg]

Added patterns for Open VPN.

[jsvd]

@Bizzelicious thanks for the contribution! can you add a few specs to show what kind of lines these patterns match? there are a lot of simple examples in the spec directory. essentially all you need is:

describe "PATTERN" do
  it "matches an open vpn log message" do
    expect(subject).to match("example of open vpn log message")
  end
end