Add CTS for BlobStoreManager.Session.openRead().

Bug: 152423769
Test: atest --test-mapping apex/blobstore
Change-Id: I517adb501bf6899dadd78c1b28c2135ae0b6f798
diff --git a/tests/BlobStoreTestUtils/src/com/android/utils/blob/DummyBlobData.java b/tests/BlobStoreTestUtils/src/com/android/utils/blob/DummyBlobData.java
index 42908be..35a6c26 100644
--- a/tests/BlobStoreTestUtils/src/com/android/utils/blob/DummyBlobData.java
+++ b/tests/BlobStoreTestUtils/src/com/android/utils/blob/DummyBlobData.java
@@ -167,7 +167,7 @@
 
         final byte[] actualBytes = new byte[lengthBytes];
         try (FileInputStream in = new ParcelFileDescriptor.AutoCloseInputStream(
-                session.openWrite(0L, 0L))) {
+                session.openRead())) {
             read(in, actualBytes, offsetBytes, lengthBytes);
         }
 
@@ -190,7 +190,7 @@
             long offsetBytes, long lengthBytes) throws Exception {
         final byte[] actualDigest;
         try (FileInputStream in = new ParcelFileDescriptor.AutoCloseInputStream(
-                session.openWrite(0L, 0L))) {
+                session.openRead())) {
             actualDigest = createSha256Digest(in, offsetBytes, lengthBytes);
         }