Always use create_homedir when we are asked to create a home directory
in the User class. Don't use the -m and -k parameters from
useradd / luseradd as they behave differently with respect to
preexisting home directories. Instead always specify -M to ensure
that useradd / luseradd do not try to create the home directory.
This does not change potential different behaviours in child classes
of the User class.
Consider the new umask option from #73821 in create_homedir as well as
we do not let luseradd / useradd create the home directory any longer.
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