[PROPOSAL] backport GEODE-8174 to 1.13 and 1.12

[Udo Kohlmeyer]

Hi there Geode Dev,

I would like to request a back port of a critical issue in the 
JCAConnectionManager. This issue manifests itself as a 
ConcurrentModificationException when trying to close a connection.

SHA: bef07b34131abddb8c0f04e0ab6a48f1daac991d

—Udo