Implement a clear return and exception strategy

[fsimonis]

Currently, it is not clear what the return values of some of the functions are and which exceptions they may throw.
As a direct result, the local_tests fail due to exceptions leaking down to the main.

My suggestion is:

Tests run as units that return whether they passed as a bool. They don't throw expected exceptions such as problems during the test itself.
Internal errors and failure reasons are logged.

My suggestion for the internal handling 1

Internal exceptions are of type SystemTestException and have one of the following 3 types all inheriting from the aforementioned class:

• STBuildException when something during the build phase went wrong
• STRunException when something during the actual test case went wrong
• STValidateException when something during the validation went wrong

My suggestion for the internal handling 2

Internal exceptions are treated in place. Every function returns a success state as a bool and logs all reasons for a failure.