Another command already in progress error under heavy load

During periods of heavy query load and high IOPS, the following error occurs: "_another command is already in progress_." This error is preceded by multiple query timeouts, prompting Citus to send cancel requests to the workers. The PR introducing connection reuse also highlights this issue.

https://github.com/citusdata/citus/commit/24e06af6d20eb992b1fdb7b2d96b13a12750595e