[Feature] Warning for running specs with cnfs present

[kosstennbl]

Is your feature request related to a problem? Please describe.
Spec tests behave incorrectly in some cases when any CNFs are already installed. That could cause unexpected and hardly traceable errors on the spec run.

Describe the solution you'd like
I propose printing a warning for the user during the initial stages of the spec run (probably somewhere before the Testsuite build). This will help avoid such situations and provide the user with information so they can react accordingly.