pgbench: doExecuteCommand -> executeMetaCommand
The new function is only in charge of meta commands, not SQL commands.
This change makes the code a little clearer: now all the state changes
are effected by advanceConnectionState. It also removes one indent
level, which makes the diff look bulkier than it really is.
Author: Fabien Coelho
Reviewed-by: Kirk Jamison
Discussion: https://postgr.es/m/alpine.DEB.2.21.
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