applypatch: Add testcases for applypatch executable.

Refactor applypatch/main.cpp into libapplypatch_modes so that we can add
testcases.

Some changes to applypatch/main.cpp:
 - Replace char** argv with const char**;
 - Use android::base::Split() to split ":";
 - Use android::base::ParseUInt().

Bug: 32383590
Test: Unit tests pass, install-recovery.sh works.

Change-Id: I44e7bfa5ab717d439ea1d0ee9ddb7b2c40bb95a4

applypatch/applypatch_main.cpp

@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "applypatch_modes.h"
+
+// This program (applypatch) applies binary patches to files in a way that
+// is safe (the original file is not touched until we have the desired
+// replacement for it) and idempotent (it's okay to run this program
+// multiple times).
+//
+// See the comments to applypatch_modes() function.
+
+int main(int argc, char** argv) {
+    return applypatch_modes(argc, const_cast<const char**>(argv));
+}