hwid: Revises the structure of the RuleContext class.

This CL flattens the `hwid` property in a rule context object into
`database`, `bom` and `mode`.  The final goal is to deprecate the
class `common.HWID`.

TEST=make test
BUG=chromium:689944

Change-Id: Ia1a2dacfbe5c9640e44cd01d935add86a7f7dd12
Reviewed-on: https://chromium-review.googlesource.com/845478
Commit-Ready: Yong Hong <yhong@google.com>
Tested-by: Yong Hong <yhong@google.com>
Reviewed-by: Yong Hong <yhong@google.com>
diff --git a/py/gooftool/commands.py b/py/gooftool/commands.py
index 97d5359..4704f35 100755
--- a/py/gooftool/commands.py
+++ b/py/gooftool/commands.py
@@ -125,7 +125,7 @@
 
 _hwdb_path_cmd_arg = CmdArg(
     '--hwdb_path', metavar='PATH',
-    default=hwid_utils.DEFAULT_HWID_DATA_PATH,
+    default=hwid_utils.GetDefaultDataPath(),
     help='Path to the HWID database.')
 
 _hwid_status_list_cmd_arg = CmdArg(