GEODE-4147: Add variability to client rebalance logic.

[PivotalSarge]

I moved the application of the variance from the pool implementation to the connection manager implementation to avoid impacting too much of the code, which lead to some failing tests.

For some reason the combination of IntelliJ and Spotless expanded some wildcard import statements but I left those as-is.

@upthewaterspout @bschuchardt @WireBaron @galen-pivotal

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[bschuchardt]

Looks good to me

[WireBaron]

It still seems odd to me that this doesn't have an equal chance of returning the original value. That being said, this all looks correct.