Fix build system so that ktest-tool and klee-stats can be installed
under release build.

The problem is that under release build the install command is told
to strip symbols from the tools. It tries to do this for the python
scripts and fails.

This commit hacks this by requesting that symbols are not stripped
from the python scripts.
Fixed race condition in parallel build where a symbolic link
(for klee-uclibc)
would be created before the destination directory existed.