tests: run virshtest independent of current pwd
tests: run virshtest independent of current pwd

virshtest execves the virsh binary. Make sure that it finds the binary's
location independent of the current working directory by specifying the
absolute path as determined by the build environment.

Reviewed-by: Marc Hartmayer <7bafc8cd4e6394916d396e4f8cde69753be8d066@linux.vnet.ibm.com>
Reviewed-by: Boris Fiuczynski <2648abdd55bfebf313fd324b464b047e6eea300e@linux.vnet.ibm.com>
Signed-off-by: Bjoern Walk <40545c009452f40d2ae0bbfbd987b332d274d328@linux.vnet.ibm.com>

crobinso/libvirt,libvirt/libvirt,andreabolognani/libvirt,nertpinx/libvirt,zippy2/libvirt,zippy2/libvirt,andreabolognani/libvirt,jardasgit/libvirt,crobinso/libvirt,eskultety/libvirt,crobinso/libvirt,crobinso/libvirt,nertpinx/libvirt,eskultety/libvirt,jardasgit/libvirt,andreabolognani/libvirt,nertpinx/libvirt,nertpinx/libvirt,jfehlig/libvirt,eskultety/libvirt,olafhering/libvirt,jfehlig/libvirt,eskultety/libvirt,libvirt/libvirt,jardasgit/libvirt,nertpinx/libvirt,zippy2/libvirt,jfehlig/libvirt,zippy2/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,libvirt/libvirt,olafhering/libvirt,libvirt/libvirt,eskultety/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,olafhering/libvirt,jfehlig/libvirt,olafhering/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,jardasgit/libvirt