Fix the bug that consul is always in the leaving state

[yangjunmyfm192085]

Fix: #662
The function handleNodeJoin is used to set member.Status = StatusAlive, and the function handleNodeJoinIntent is used to set member.statusLTime = joinMsg.LTime.
Unfortunately, the two are not in sync. If set member.statusLTime directly in handleNodeJoinIntent, will get wrong results. As a result, the member state we see has always been leaving
e.g.
We have 3 members A B and C in our cluster, Both B and C join the cluster through A.

• We do leave and start operations on node B
• When node A updates member.statusLTime of B to the latest value in the function handleNodeJoinIntent, member.Status may still be left.
• When A sends its member status to C through pushPullMsg, C recognizes that the status of B is leave and marks member .statusLTime is the received value + 1 incorrectly.
• C refreshes the status of member B as leaving, and marks member.statusLTime as member.statusLTime as the received value +1
• The state of B in C continues to be leaving eventually

[hashicorp-cla]

All committers have signed the CLA.

[chymy]

/lgtm

[chymy]

/assign @rboyer

[yangjunmyfm192085]

/cc @rboyer

[kemko]

@rboyer ?...