Enable shell tests

We need to use sudo: required, and dist: trusty to avoid old versions of
bash in travis which don't support the -n argument to the `wait` shell
built-in.

We had to disable the -e checks in etcd.sh since the killall || killall
parts were causing those to trigger in travis.

test/shell/etcd.sh

@@ -1,7 +1,4 @@
 # NOTE: boiler plate to run etcd; source with: . etcd.sh; should NOT be +x
-set -o errexit
-set -o nounset
-set -o pipefail
 cleanup ()
 {
 	killall etcd || killall -9 etcd || true	# kill etcd