Stacktraces fail to be generated when MaxScale is run from the terminal

If MaxScale is run from the terminal and the executable is found with a PATH lookup, the name of the executable in dladdr() will be relative instead of absolute. This causes a problem where the stacktraces are not generated and end up printing the previous stack frame's address until another valid frame is found.

The problem can be solved by reading the actual executable file name from /proc/self/exe and passing that to addr2line.