test_driver: implement virDomainGetDiskErrors
test_driver: implement virDomainGetDiskErrors

Return the number of disks present in the configuration of the test
domain when called with @errors as NULL and @maxerrors as 0.

Otherwise report an error for every second disk, assigning available
error codes in a cyclic order.

Signed-off-by: Ilias Stamatis <3ef66acc2700f2eb6746a592b321628ebd41accf@gmail.com>
Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>

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