Notification for non-adopotable disks shouldn't be snoozed

Note if an adoptable SD is mounted as an external disk, it'll still be
snoozeable.  I *think* it's reasonable, as long as the sd card is inside
the device.

Bug 21898269

Change-Id: I0aaa6c85f9db84e3f30d3b0b485a35a5abef84e8