Multiple dracut module install script cleanups

• Replaced intances of dracut_install with inst_simple
• Removed calls to test -x mark_hostonly because the function is an

inbuilt dracut function

• Removed redundant installation of systemd-ask-password and

systemd-tty-ask-password-agent because they are already installed by
the systemd module. There is no need to install them again

• Removed multiple calls to the mark_hostonly function because the

inst_simple has a command-line switch for it

• Cleaned up the installation of the zpool.cache, vdev_id.conf and

hostid files to make the logic easier to follow

• Cleaned up and simplified the systemd service installation logic by

invoking systemctl instead of creating symlinks manually

• Replaced various hard-coded paths with dracut equivalents to better

conform with expected dracut behaviour

• Removed redundant call to mkdir (inst_simple creates the parent

directory if it does not exist on the destination initrd)

Reviewed-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Reviewed-by: Andrew J. Hesford <ajh@sideband.org>
Signed-off-by: Savyasachee Jha <hi@savyasacheejha.com>
Closes #13010