If a home directory is specified for an existing user that does
not have one, `usermod` does not create one. This case is now
detected and `mkhomedir_helper(8)` is run inside the chroot to
create the home dir. In Fedora this utility is provided by the
`pam` package so this is now installed in the corresponding
tests together with a new user that simulates the aforementioned
scenario.
Enahnce the stage description: drop an superflous line and add
a description for the home-dir scenario.