Make /events API send headers immediately

Go's net/http API does not send headers until the first call to
ResponseWriter.Write().  Ordinarily, this is fine, because in most
cases, responses are returned immediately.  However, for the events
API, nothing is written until some event is sent, which causes
timeouts and/or hangs in some HTTP client APIs, which wait for headers
before returning from the "make request" call.
Added explicit Flush method to utils.WriteFlusher
Introduce failing test case for #2089
Added some more colors and animals to increase the pool
Create new network on dead ghosts on restart.

Fixes #2089
Remove duplicate titles in changelog entries of v0.6.5
Merge pull request #2537 from jamtur01/more_names

Added some more colors and animals to increase the pool
Merge pull request #2542 from oguzbilgic/changelog-0.6.5

Remove duplicate titles in changelog entries of v0.6.5
Merge pull request #2427 from thequux/send-headers-immediately

Make /events API send headers immediately
Merge pull request #2409 from pnasrat/2089-fix-restart-runtime-error

Fix restart runtime error with ghost container networking