StatFsTest: allow no available blocks/bytes for system

CTS fails for block-based system partitions using squashfs
because there are no available blocks/bytes on this read-only
partition.

Bug: 23315826
Change-Id: I4627599835669e3d1efb830bf0158dd77dda8411
diff --git a/tests/tests/os/src/android/os/cts/StatFsTest.java b/tests/tests/os/src/android/os/cts/StatFsTest.java
index 67afde9..a0653fd 100644
--- a/tests/tests/os/src/android/os/cts/StatFsTest.java
+++ b/tests/tests/os/src/android/os/cts/StatFsTest.java
@@ -46,15 +46,15 @@
         assertTrue(stat.getBlockSize() > 0);
         assertTrue(stat.getBlockCount() > 0);
         assertTrue(stat.getFreeBlocks() >= stat.getAvailableBlocks());
-        assertTrue(stat.getAvailableBlocks() > 0);
+        assertTrue(stat.getAvailableBlocks() >= 0);
 
         assertTrue(stat.getBlockSizeLong() > 0);
         assertTrue(stat.getBlockCountLong() > 0);
         assertTrue(stat.getFreeBlocksLong() >= stat.getAvailableBlocksLong());
-        assertTrue(stat.getAvailableBlocksLong() > 0);
+        assertTrue(stat.getAvailableBlocksLong() >= 0);
 
-        assertTrue(stat.getFreeBytes() > 0);
-        assertTrue(stat.getAvailableBytes() > 0);
+        assertTrue(stat.getFreeBytes() >= 0);
+        assertTrue(stat.getAvailableBytes() >= 0);
         assertTrue(stat.getTotalBytes() > 0);
     }
 }