.travis, build: autodelete old unstable archives (#13867)

This commit adds a build step to travis to auto-delete unstable archives older than
14 days (our regular release schedule) from Azure via ci.go purge.

The commit also pulls in the latest Azure storage code, also switching over from
the old import path (github.com/Azure/azure-sdk-for-go) to the new split one
(github.com/Azure/azure-storage-go).

vendor/github.com/dgrijalva/jwt-go/ecdsa_utils.go

@@ -0,0 +1,67 @@
+package jwt
+
+import (
+	"crypto/ecdsa"
+	"crypto/x509"
+	"encoding/pem"
+	"errors"
+)
+
+var (
+	ErrNotECPublicKey  = errors.New("Key is not a valid ECDSA public key")
+	ErrNotECPrivateKey = errors.New("Key is not a valid ECDSA private key")
+)
+
+// Parse PEM encoded Elliptic Curve Private Key Structure
+func ParseECPrivateKeyFromPEM(key []byte) (*ecdsa.PrivateKey, error) {
+	var err error
+
+	// Parse PEM block
+	var block *pem.Block
+	if block, _ = pem.Decode(key); block == nil {
+		return nil, ErrKeyMustBePEMEncoded
+	}
+
+	// Parse the key
+	var parsedKey interface{}
+	if parsedKey, err = x509.ParseECPrivateKey(block.Bytes); err != nil {
+		return nil, err
+	}
+
+	var pkey *ecdsa.PrivateKey
+	var ok bool
+	if pkey, ok = parsedKey.(*ecdsa.PrivateKey); !ok {
+		return nil, ErrNotECPrivateKey
+	}
+
+	return pkey, nil
+}
+
+// Parse PEM encoded PKCS1 or PKCS8 public key
+func ParseECPublicKeyFromPEM(key []byte) (*ecdsa.PublicKey, error) {
+	var err error
+
+	// Parse PEM block
+	var block *pem.Block
+	if block, _ = pem.Decode(key); block == nil {
+		return nil, ErrKeyMustBePEMEncoded
+	}
+
+	// Parse the key
+	var parsedKey interface{}
+	if parsedKey, err = x509.ParsePKIXPublicKey(block.Bytes); err != nil {
+		if cert, err := x509.ParseCertificate(block.Bytes); err == nil {
+			parsedKey = cert.PublicKey
+		} else {
+			return nil, err
+		}
+	}
+
+	var pkey *ecdsa.PublicKey
+	var ok bool
+	if pkey, ok = parsedKey.(*ecdsa.PublicKey); !ok {
+		return nil, ErrNotECPublicKey
+	}
+
+	return pkey, nil
+}