tests: virstorage: Add tests for NBD URI style syntax over UNIX
tests: virstorage: Add tests for NBD URI style syntax over UNIX

Add few test cases for nbd+unix style URIs with few corner cases.

The NBD URI syntax is documented at
https://github.com/NetworkBlockDevice/nbd/blob/master/doc/uri.md

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Reviewed-by: Eric Blake <a9da18479c871fe903d9590822cfe2629c6a4d11@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

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