SOLR-15715: coordinator role

[noblepaul]

trafficstars

WIP

[dsmiley]

use ! rather than == false, no?

Using == false is especially prevalent in Lucene and it's a deliberate choice; I prefer it as well. It reads in a more obvious way. The single exclamation mark on the left of an expression is visually subtle. A bug was found once long ago where this was deemed the root cause.

[noblepaul]

closing in favor of #716