tests: add multi key encryption/decryption test, new way for fake passphrase cache

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/PgpDecryptVerify.java

@@ -84,7 +84,7 @@ public class PgpDecryptVerify extends BaseOperation {
     private boolean mDecryptMetadataOnly;
     private byte[] mDecryptedSessionKey;
 
-    private PgpDecryptVerify(Builder builder) {
+    protected PgpDecryptVerify(Builder builder) {
         super(builder.mContext, builder.mProviderHelper, builder.mProgressable);
 
         // private Constructor can only be called from Builder

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/PgpSignEncrypt.java

@@ -95,7 +95,7 @@ public class PgpSignEncrypt extends BaseOperation {
         }
     }
 
-    private PgpSignEncrypt(Builder builder) {
+    protected PgpSignEncrypt(Builder builder) {
         super(builder.mContext, builder.mProviderHelper, builder.mProgressable);
 
         // private Constructor can only be called from Builder