fileio: make parse_env_file() return number of parsed items

fileio: make parse_env_file() return number of parsed items

This commit introduces possibility to call parse_env_file_internal() and hand
over extra argument where we will accumulate how many items were successfully
parsed and pushed by callback. We make use of this in parse_env_file() and
return number of parsed items on success instead of always returning zero.

As a side-effect this commit should fix bug that locale settings in
/etc/locale.conf are not overriden by options passed via kernel command line.