Rename lxc_password to lxc_root_password for consistency with the new
lxc_user_password (replaces the previously bare 'password' variable in
post-clone.yml, which silently collided with any same-named caller var).
Add lxc_user_name (default: admin) so the non-root account managed in
post-clone.yml is no longer hardcoded. Apply default(omit) to the root
password in create.yml so it is genuinely optional as documented.
BREAKING CHANGE: callers passing lxc_password or a bare 'password' var
must rename to lxc_root_password and lxc_user_password respectively.
patrick