Add empty keystore2 crate

Adds an empty crate with a build config for libkeystore2 and the
keystore2 test.

Also add a TEST_MAPPING file setting up keystore2_test as presubmit
test.

Bug: 160623310
Test: keystore2_test
Change-Id: I2cda9a74a43422453cf5d1d44867107c9f0292bf
diff --git a/keystore2/src/lib.rs b/keystore2/src/lib.rs
new file mode 100644
index 0000000..97c1839
--- /dev/null
+++ b/keystore2/src/lib.rs
@@ -0,0 +1,15 @@
+// Copyright 2020, 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.
+
+//! This crate implements the Android Keystore 2.0 service.