reporter_kbpki: suppress username popup errors for auto-lookups
reporter_kbpki: suppress username popup errors for auto-lookups

"gemfile", "objects" and "devfs" have all been seen in the wild.
These are reserved usernames so there should never be a real account
with those names.

Issue: KBFS-825.

keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/client