switch to new go-acme imports from xenolf. Fix api changes (#540)

* switch to new go-acme imports from xenolf. Fix api changes

* update many vault related dependencies

vendor/github.com/go-acme/lego/challenge/provider.go

@@ -0,0 +1,28 @@
+package challenge
+
+import "time"
+
+// Provider enables implementing a custom challenge
+// provider. Present presents the solution to a challenge available to
+// be solved. CleanUp will be called by the challenge if Present ends
+// in a non-error state.
+type Provider interface {
+	Present(domain, token, keyAuth string) error
+	CleanUp(domain, token, keyAuth string) error
+}
+
+// ProviderTimeout allows for implementing a
+// Provider where an unusually long timeout is required when
+// waiting for an ACME challenge to be satisfied, such as when
+// checking for DNS record propagation. If an implementor of a
+// Provider provides a Timeout method, then the return values
+// of the Timeout method will be used when appropriate by the acme
+// package. The interval value is the time between checks.
+//
+// The default values used for timeout and interval are 60 seconds and
+// 2 seconds respectively. These are used when no Timeout method is
+// defined for the Provider.
+type ProviderTimeout interface {
+	Provider
+	Timeout() (timeout, interval time.Duration)
+}