lxd/api/cluster: Updates clusterPutJoin to handle per server certificates
lxd/api/cluster: Updates clusterPutJoin to handle per server certificates

 - Leave server cert in cluster trust store so that cluster members trust new member after join complete.
 - Preload local trust store with existing cluster server certificates before completing join, so that cluster leader can connect to new member.
 - Refresh local trusted certs before join is completed so that preloaded certificates take effect.
 - Call cluster.UpdateTrust in clusterPutJoin To ensure our trusted certificate is of the correct name and type for cluster operation.
 - Ensures we can find the trusted certificate for a cluster member by name.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

stgraber/lxd,hallyn/lxd,atxwebs/lxd,stgraber/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,atxwebs/lxd,stgraber/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,atxwebs/lxd,stgraber/lxd,stgraber/lxd,hallyn/lxd,stgraber/lxd,atxwebs/lxd,hallyn/lxd,stgraber/lxd,lxc/lxd