Joerg, sorry but I don't know what that error means or why you're getting it. I don't recall needing to do anything special to get chrpath installed (but you know how the memory is). But the whole installer script for Linux is brand new (to QGC and myself), so I wouldn't be surprised if there's some issues, especially on different flavors. Yet another thing to track down... Changing the rpath is important though, the final executable won't be truly portable w/out this step.
You should not need to rebuild the whole thing just to run "make install" at the end for testing solutions (it's mostly just copying files around at this stage, not building anything). Also the install step should be runnable from QtCreator as I mentioned before. Perhaps the syntax was wrong... on my Windows setup it's "make release install" to build and install at once, instead of "make all install" like in my Linux screenshot from earlier. It would be good to "fix" that if possible so it works as intended. One can also create a new build type in Creator for only installing, so just "make install" w/out running qmake first.
The advantage of doing everything via Creator is that it ensures the operating environment is set up correctly for the Qt version being used. If there are multiple Qt versions installed (including any the OS itself installed, eg. KDE relies heavily on Qt), building directly from a command line can lead to confusion.
As for quatosTool, same deal... no idea why it doesn't work on your system. Could be a bitness thing or who knows what. You could try building it yourself since you already have all the tools installed. All the latest sources are here:
https://github.com/AutoQuad/utilitiesCheers,
-Max