Cleanup to use java.util.Base64

jdk8 has java.util.Base64 to define a standard API for base64 encoding/decoding. It would be good to investigate whether this API could be used in the security components, providers and regression tests.

% cd /jdk/src/share/classes/sun/security
% find ./ -name "*.java" | xargs egrep -l "BASE64Encoder |BASE64Decoder"
./provider/X509Factory.java
./util/SignatureFileVerifier.java
./util/ManifestEntryVerifier.java
./x509/X509CertImpl.java
./tools/keytool/Main.java
./tools/jarsigner/Main.java
./pkcs10/PKCS10.java


% cd jdk/test/sun/security
% find ./ -name "*.java" | xargs egrep -l "BASE64Encoder |BASE64Decoder"
./krb5/auto/HttpNegotiateServer.java
./ssl/sun/net/www/protocol/https/HttpsURLConnection/ProxyTunnelServer.java
./ssl/com/sun/net/ssl/internal/www/protocol/https/HttpsClient/ProxyTunnelServer.java
./ssl/com/sun/net/ssl/internal/ssl/SSLContextImpl/TrustTrustedCert.java
./ssl/com/sun/net/ssl/internal/ssl/SSLContextImpl/MD2InTrustAnchor.java
./ssl/com/sun/net/ssl/internal/ssl/X509TrustManagerImpl/BasicConstraints.java
./ssl/com/sun/net/ssl/internal/ssl/X509TrustManagerImpl/SelfIssuedCert.java
./ssl/javax/net/ssl/TLSv12/ShortRSAKeyGCM.java
./ssl/javax/net/ssl/TLSv12/ShortRSAKey512.java
./ssl/javax/net/ssl/ServerName/SSLSocketSNISensitive.java