amend! Simplify root logger configuration

Simplify root logger configuration (canonical#4435)

The root logger gets configured at various stages of cloudinit execution.
Some changes occur while importing cloudinit.log, which causes side effects
in any project using cloudinit as a library (Ubuntu Pro, etc). These
modifications do not require change during runtime and can take place as
an early setup task in cloudinit.cmd.main::main().

Simplify this code, relocate logger configuration code to a function in
cloudinit.log, set the callsite in cloudinit.cmd.main::main().

Also add context to logging configuration code.