buffet: Added minimal role into command definition

Possible values "viewer", "user", "owner", "manager".
Default minimal role is set to "user".
Role check is not yet implemented.

BUG=brillo:808
TEST=`FEATURES=test emerge-gizmo buffet`

Change-Id: I74d16c24618b50de1e7a2ffa37d7aef36978a38a
Reviewed-on: https://chromium-review.googlesource.com/274117
Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>
diff --git a/buffet/buffet.gyp b/buffet/buffet.gyp
index 8bcc7d8..b91bdef 100644
--- a/buffet/buffet.gyp
+++ b/buffet/buffet.gyp
@@ -35,6 +35,7 @@
         'commands/prop_values.cc',
         'commands/schema_constants.cc',
         'commands/schema_utils.cc',
+        'commands/user_role.cc',
         'device_registration_info.cc',
         'dbus_bindings/org.chromium.Buffet.Command.xml',
         'dbus_bindings/org.chromium.Buffet.Manager.xml',