testing/testcase: check executables are not linked with system libraries

Except a short whitelist of system libraries, we should have always set
rpath so that the slapos version of the library is used.

We had issues with components which where compiled with slapos version
of openssl but linked without rpath. At runtime they were using system
openssl.

Rewrite our complex grep shell pipeline in python, with a function
parsing ldd output so that we can check not only for not found dynamic
libraries, but also for libraries that are found outside of slapos
library dirs.

This also fixes problems that this grep pipeline did not support paths
with spaces in their names.