List filesystem and swift as known glance stores

Glance used to default to include all stores as "known" but has now
switched to only knowing the filesystem store by default. As of
I82073352641d3eb2ab3d6e9a6b64afc99a30dcc7

Change-Id: I10aebbd7c6969c6d95579f3b266e03501a7bedb7
Closes-Bug: #1290969