Reporting/Collector: add max-children argument

Add option to limit the count of child threads to import the transactions.
If the number is exceeded the next import will block until one thread is
ready.
Reporting/Collector: fix python2.4 compatibility
Client/Tools/YUM: fix whitespace errors
Client/Tools/YUM: compareEVR is in rpmUtils.miscutils
travis-ci: enable system site packages

There is no easy way to install yum with pip. So we need the system site
packages to test the YUM plugin.
Merge branch 'yum-fix-syntax' of https://github.com/AlexanderS/bcfg2
Merge branch 'reporting-limit-children' of https://github.com/AlexanderS/bcfg2