Use try with resources in BackupManagerService

Resources are not handled in a consistent manner, or even consistently
closed.

Bug: 36850431
Test: adb shell am instrument -w -e package com.android.server.backup com.android.frameworks.servicestests/android.support.test.runner.AndroidJUnitRunner
Change-Id: I9ca2bd8d532af385174a107ee7fbe113575c5bbb
1 file changed