ini-parser: add libsys_config_parse_by_section()

ini-parser: add libsys_config_parse_by_section()

The original function, config_parse(), parses configuration file line by
line. Due to this, a parser, which is registered by the config_parse(),
can hardly handle out-of-ordered section/property or multiple sections
with same name.

The libsys_config_parse_by_section() now parses configuration file
by section. Therefore a parser can now find whole properties of a
section when the section is conveyed to the parser.

Change-Id: I08f09e2f6aefabea497393edb3c1f88dbe2d8850
Signed-off-by: Youngjae Cho <y0.cho@samsung.com>