Follow "atomic" to "group" refactoring.

Remove noisy logging about UIDs that are relying on default cache
quota of 64MiB.

Move away from yucky old statfs() and use statvfs() instead.

Test: /data/nativetest/installd_cache_test/installd_cache_test
Bug: 35812899, 35684969, 36482620
Change-Id: I3d68da97eac2ebcda489bdf9d27061cac5b3f7cc
diff --git a/cmds/installd/CacheItem.h b/cmds/installd/CacheItem.h
index afbb15d..84b77aa 100644
--- a/cmds/installd/CacheItem.h
+++ b/cmds/installd/CacheItem.h
@@ -31,8 +31,8 @@
 
 /**
  * Single cache item that can be purged to free up space. This may be an
- * isolated file, or an entire directory tree that should be atomically
- * deleted.
+ * isolated file, or an entire directory tree that should be deleted as a
+ * group.
  */
 class CacheItem {
 public:
@@ -46,7 +46,7 @@
 
     short level;
     bool directory;
-    bool atomic;
+    bool group;
     bool tombstone;
     int64_t size;
     time_t modified;