run: use portable shell

run: use portable shell

Nothing in run required bash, except for the shebang.  On systems
where /bin/bash doesn't exist (I hit it on FreeBSD), using /bin/sh
instead fixes a 'make check' failure:
gmake[3]: Entering directory `/usr/home/dummy/libvirt/python'
  GEN    check-local
/usr/local/bin/bash: ../run: /bin/bash: bad interpreter: No such file or directory

* run.in: Use /bin/sh, not bash.