Explicitly close file stream when initializing quotas.

When the device boots and the StorageStatsService is initialized, we
load the last calculated cache quotas from a file. We were never closing
the FileInputStream and leaked a resource.

By using try-with-resources, we can avoid that.

Bug: 128920416
Test: Manual -- did not crash on a phone that booted a few times.
Change-Id: Ib85e571ddf033caf63eef7c69a91336dad1b55bc