sys-apps/baselayout: handle Prefix-related paths more robustly.

sys-apps/baselayout: handle Prefix-related paths more robustly.

  commit 6d45b94abca08b1c124e11 fails with a corner case that EPREFIX
  contains substring /usr.  This commit fix it by using the well tested
  hprefixify from prefix.eclass.

  Also apply hprefix to other files to simplify the ebuild.  Tested on
  both Prefix and vanilla Gentoo.

  Move the host PATHs to /etc/env.d/99host.

  For Prefix, ROOTPATH will always be used, because it is almost a single
  user system.

Package-Manager: Portage-2.3.3, Repoman-2.3.1