This looks a bit weird (two subprofiles become a bit more
tightly coupled) but in fact install2 does depend on stage1,
and if stage1 doesn't create squashcfg.mk then install2 is
just fine with defaults (provided they fit the installer kernel
used).  A proper mkimage test infrastructure might be handy though.

Also there:
- 01-initfs: partial cleanup (bootsplash is obsolete anyways)
- regarding 03-test-kernel's errorlevel test:
  if 0, 1 and 2 need to be distinguished, "!" MUST NOT be used
  as it negates so that 0 becomes 1 and the rest becomes 0