Allow forcing cert reissuance (#28)

Refreshing the cert should force renewal as opposed to returning
early if the SANs aren't changing. This is currently breaking refresh
of expired certs as per:
https://github.com/rancher/k3s/issues/1621#issuecomment-669464318

Signed-off-by: Brad Davidson <brad.davidson@rancher.com>

cert/io.go

@@ -34,15 +34,15 @@ func CanReadCertAndKey(certPath, keyPath string) (bool, error) {
 	certReadable := canReadFile(certPath)
 	keyReadable := canReadFile(keyPath)
 
-	if certReadable == false && keyReadable == false {
+	if !certReadable && !keyReadable {
 		return false, nil
 	}
 
-	if certReadable == false {
+	if !certReadable {
 		return false, fmt.Errorf("error reading %s, certificate and key must be supplied as a pair", certPath)
 	}
 
-	if keyReadable == false {
+	if !keyReadable {
 		return false, fmt.Errorf("error reading %s, certificate and key must be supplied as a pair", keyPath)
 	}