virsh: Clear vsh last error during virshCommandOptVolBy
virsh: Clear vsh last error during virshCommandOptVolBy

https://bugzilla.redhat.com/show_bug.cgi?id=1529256

If one of the virStorageVolLookupBy{Key|Name|Path} succeeds and
we have a @vol, then clear the last libvirt error; otherwise, a
subsequent "other" failure may cause vshReportError to erroneously
report the wrong error as well as a reported 'vshError' error that
caused the failure.

Signed-off-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>

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