use existing transporter mutex

Second half of the fix for this bug.

This patch forces a heartbeat to be sent and will wait (a little while)
for replies. This way we can get

> all status
X starting
Y started
X started
>

which is okay as the new status comes after the old status, always.
There is the slimmest of opportunities to get output like above where only half
the cluster appears started.

This is about the best we can do with a command line interactive program.

- invalidate ndb dict cache on cluster disconnect (ClusterMgr.cpp)
- add check for correct frm on external lock when table cache is found invalid

Reset missed heartbeat count on receipt of signal from node.

This fixes a bug where that under high network load, the heartbeat packets could be
delayed, causing the appearance of node failure (due to lost heartbeats).

  Cluster failure with non started nodes can result in timedout transactions

WL1356 - Discless db node
WL1357 - sp 1-2