fix function name changed.
fix function name changed.

PR #393 has introduced a new function name. ( merged).
PR #376 was using the old name, which we merged after pr #393 and the
review was done before merging #393.

This commit just fix the name of function

dmacvicar/terraform-provider-libvirt,dmacvicar/terraform-provider-libvirt,dmacvicar/terraform-provider-libvirt