New set of assets with a Conflicts:

Better to test Conflicts: than Breaks: that have packages installed in a
transient state
Don't auto_fix installation and better exch. file

* Don't auto_fix installation so that we can detect if an installation didn't
succeed instead of assuming that the whole set of packages are installed
(if testpackage and testpackage2, with the later conflicting on the first one
were installing with auto_fix=False, only testpackage would silently be
installed)
* Rationalize the error exchange file by always creating it and display its
content if it's not empty
Add more tests for RequirementsHandler

Also, use the parameter for signaling the timeout in case of error.