Add a virKeyfilePtr object for parsing '.ini' files

Add a virKeyfilePtr object for parsing '.ini' files

The '.ini' file format is a useful alternative to the existing
config file style, when you need to have config files which
are hashes of hashes. The 'virKeyFilePtr' object provides a
way to parse these file types.

* src/Makefile.am, src/util/virkeyfile.c,
  src/util/virkeyfile.h: Add .ini file parser
* tests/Makefile.am, tests/virkeyfiletest.c: Test
  basic parsing capabilities

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>