switch from go_cfmessagebus to yagnats

Also remove stale .gitmodules.

[finishes #60352022]

Signed-off-by: Eric Malm <emalm@pivotallabs.com>
test against gnatsd

Signed-off-by: Glenn Oppegard <goppegard@pivotallabs.com>
Auto-merge remote-tracking branch 'upstream/master'