Add a ./run script for running programs from the local directory.

Add a ./run script for running programs from the local directory.

With this script you can run libvirt programs without needing to
install them first.  You just have to do for example:

  ./run ./tools/virsh [args ...]

If you are already in the tools/ subdirectory, then the following
command will also work:

  ../run ./virsh [...]

You can also run the C programs under valgrind like this:

  ./run valgrind [valgrind opts...] ./program

or under gdb:

  ./run gdb --args ./program

This also works with sudo (eg. if you need root access for libvirt):

  sudo ./run ./tools/virsh list --all

Derived from libguestfs and simplified.  The ./run script in
libguestfs is much more sophisticated:

https://github.com/libguestfs/libguestfs/blob/master/run.in