Support restart of first seed node, see #2854

* Try to first join other seed nodes before joining itself
(cherry picked from commit 679c4d313d961dfadaf0df7906241e95f3f7e816)

Conflicts:

	akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala
Merge pull request #1177 from akka/wip-2854-restart-seed1-release-2.1-patriknw

Support restart of first seed node, see #2854