Make some pkg-map errors soft

An app using pkg-map (like package-installs) might want to distinguish
between a hard error (invalid pkg-map file) and a soft error (no
mapping found). Currently this is not possible because we only return
with error values of 1.

Also printing error messages to stderror so we can still make use of
stdout data during a soft error.

Change-Id: I8bef56d3a74e8530afb8c58ac50ca3e9f7700639
Merge "Make some pkg-map errors soft"