Tolerate null on Json db load

A icehouse->juno migration issue has surfaced where
resource.properties_data is null for existing resource records.

This change fixes the Json db type to treat None the same as
the serialized JSON 'null'.

Change-Id: Ia0b9a23a7798c95fbbcba439ffb8203b50367e7c
Closes-Bug: #1383505
Make HARestarter do a proper lookup of the RefID

HARestarter is a primitive prototype that is barely maintained.  Its
implementation still dates to the era when the resource name, physical
resource ID and RefId were regularly used interchangably.

This change substitutes Stack.resource_by_refid() for the previous
(incorrect) home-grown hack, so that at least the giant red flags will be
easy to grep for.

Change-Id: I9d81dfcd5d34282c8bd83bbd98350e75c1ec0eb2
Closes-Bug: #1381136
Add some imports to hacking import_exceptions

To avoid H302 check, add most common imports to import_exceptions.
from heat.common.i18n import _
from heat.common.i18n import _LE
from heat.common.i18n import _LI
from heat.common.i18n import _LW

Change-Id: I4e4d1462d4c351e08a09d935a5a177c1d8954e06
Merge "Make HARestarter do a proper lookup of the RefID"
Merge "Tolerate null on Json db load"
Merge "Add some imports to hacking import_exceptions"