crimson/osd/heartbeat: avoid racing when connecting to peer

crimson/osd/heartbeat: avoid racing when connecting to peer

before this change, we could initialize connections to newly added peers
in parallel repeatly, if an OSD is listed in up/acting of multiple PGs
served by current OSD.

after this change, we try to add the peer to `Heartbeat.peers` first,
and then try to connect to it with the hb front/back addresses, to avoid
potential repeatly connecting to peer.

Signed-off-by: Kefu Chai <kchai@redhat.com>