Fix disconnect race.

[cheatfate]

• Fix PeerPool to use getFuture() only once when adding peer.
• Add isAlive(peer) procedure.
• Add join(peer) procedure.
• Remove useless metric (discovery).
• Add notifyAndWait() procedure which will help to avoid race while disconnecting.

[github-actions[bot]]

Unit Test Results

     12 files  ±0     744 suites  ±0   33m 19s :stopwatch: +26s 1 467 tests +1  1 465 :heavy_check_mark: +1  2 :zzz: ±0  0 :x: ±0  8 936 runs  +4  8 928 :heavy_check_mark: +4  8 :zzz: ±0  0 :x: ±0 

Results for commit 4957ae88. ± Comparison against base commit f19a497e.

:recycle: This comment has been updated with latest results.