dockertest.environment: Add support for INI config parser

this parser automatically gathers info from INI files about the subtest
configuration and prints it into the subtest documentation.

It requires #: prefix to store the value as description of following
configuration option.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
config_defaults..save_load: Modify config to work with DocGrabber

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>