Add a new move FailoverAndReplace
Add a new move FailoverAndReplace

This patch adds a new instance move, FailoverAndReplace, which promotes
the old secondary to primary and then uses a new secondary node.

This is the last move that we can do within the limitations of one node
changed per move.
andir/ganeti,onponomarev/ganeti,leshchevds/ganeti,mbakke/ganeti,yiannist/ganeti,leshchevds/ganeti,apyrgio/ganeti,dimara/ganeti,dimara/ganeti,mbakke/ganeti,onponomarev/ganeti,apyrgio/snf-ganeti,grnet/snf-ganeti,yiannist/ganeti,ganeti/ganeti,bitemyapp/ganeti,andir/ganeti,yiannist/ganeti,ganeti/ganeti,mbakke/ganeti,apyrgio/snf-ganeti,grnet/snf-ganeti,leshchevds/ganeti,ganeti-github-testing/ganeti-test-1,ganeti/ganeti,bitemyapp/ganeti,ganeti-github-testing/ganeti-test-1,apyrgio/ganeti,andir/ganeti