Noux GDB: resolve '..' in run script

If the path of a Genode source file (as extracted from the binary test
application) contains a part like '/a/b/../' where '/a' exists, but '/a/b'
does not exist anymore, 'tar' complains. With this patch, the run script
normalizes the path before calling 'tar'.

Fixes #875.
GDB monitor: move GDB commands into separate file

This patch moves the GDB commands to set a breakpoint in the 'main()'
function into a separate file that can be included from other run scripts.

Fixes #876.
run: make 'is_qemu_available' return false for Linux

Fixes #862.