.travis.yml: add IRC notifications for build failures

.travis.yml: add IRC notifications for build failures

I'm trying to avoid spamming the IRC channel (not overly likely as
builds take a while). So failure will always be reported but if the
build continues to work then the IRC notifications will be quiet.

Note any GitHub based repository with Travis enabled will use this
notification. If it proves to be too spammy we may want to ask users not
to use Travis themselves although this seems sub-optimal.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>