Relax host init parser to work with the build system

It's not going to be possible to safely assume $OUT has the right init
scripts to be parsed at a given point, so instead we fall back to
parsing init scripts individually.

This isn't a full revert of the previous commits.  We retain parsing
correctness of the 'import' statements and we retain using the new
host side property functionality.

Also, fix a bug where main was not actually returning -1 on failure

Bug: 36970783
Test: testing individual files still works correctly
Change-Id: I4ae5620f234caa08993deb2c30825904a75f6654