Fix a couple of INI whitespace bugs

* iniset() bails if no section or option (attribute) is supplied
* merge_config_file() properly skips lines with only whitespace

* Also split the ini-tests into their own script

Bug 1257954

Change-Id: Ie31c5bd0df8dfed129fbcf1e37228aaf25e9305d
Merge branch 'local-conf-whitespace' into dt-test