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##### Summary
Fix: #4756
`python.d.plugin` updates:
* remove `retries` option
* make `penalty` configurable (enabled by default, max is 10 minutes)
> penalty indicates whether to apply penalty to update_every in case of failures.
> Penalty will increase every 5 failed updates in a row. Maximum penalty is 10 minutes.
> penalty: yes
##### Component Name
`python.d.plugin`
##### Additional Information
* Add proxysql python plugin
* fix codacy issue
* add proxysql to python.d.conf
* add monitor for commands
* add default config options for admin user
* add commands histogram and improve queries
* remove duplicated variable name
* add proxysql plugin to python.d/Makefile
* rename id variable
* change default port from 3306 to 6032
* add proxysql section to the readme
* Formatting
* fix typo
* change name of charts
* use format() for concatination
* don't make methods protected
* format multiline containers
* fix format placeholders
* fix long lines
* Add configuration notice
* increase the version
