Allow clock drifts up to 10. (#58)

In SCIONLab the clocks are not well synchornized. We allow up to 10 seconds difference
among clocks in different machines.
This particular patch relies on  instead of modifying the
default values.

(cherry picked from commit 692af45)

Author: juagargi

go/lib/infra/modules/trust/verifier.go

@@ -42,8 +42,8 @@ type verifier struct {
 // control-plane PKI certificates through infra.Verifier interface.
 func NewVerifier(provider CryptoProvider) infra.Verifier {
 	return &verifier{
-		AllowSkew: 1 * time.Second,
-		MaxAge:    2 * time.Second,
+		AllowSkew: 10 * time.Second, // XXX scionlab: allow up to 10s skew
+		MaxAge:    10 * time.Second, //     "
 		Store:     provider,
 	}
 }