Improve local exporter log message during rolling upgrade

[elasticmachine]

Original comment by @luizgpsantos:

During a rolling upgrade the local exporter prints this log message even when the recent upgraded node has x-pack installed:

[2018-03-08TXX:XX:XX,XXX][INFO ][o.e.x.m.e.l.LocalExporter] waiting for elected master
node [{node1}{oy2s7SAsTd-wWcUvIlZ1Qe}{nROAp2n6Rg2qaMhUq43sta}{10.10.10.1}{10.10.10.1:9300}
{ml.machine_memory=128558536, ml.max_open_jobs=20, ml.enabled=true}] to setup local exporter 
[default_local] (does it have x-pack installed?)

Any untypical message during an upgrade can scary the user. Can we think of a more straightforward message that points the version divergence?

[elasticmachine]

Original comment by @jaijhala:

The log info is a bit misleading, I noticed it as well.
Related discussion -> #28974

[Rohlik]

I also find this log in my logfile.

[dakrone]

Internal monitoring has been deprecated for quite a while, and we're no longer doing any active development on it. I'm going to close this issue.