Add logging capability to code parser

Helps to get more information when something goes wrong.
Can be enabled by setting QT_LOGGING_RULES to
qtc.autotest.testcodeparser.debug=true

Change-Id: Ic168029912f8af509d6a822440658225c7f04eab
Reviewed-by: Niels Weber <niels.weber@theqtcompany.com>