lvresize: fix zero size extension

lvresize: fix zero size extension

Commit ca878a3426197b629c76e98cfc049948da470cd7 changed behavior
or resize operation. Later the code has been futher changed
to skip fs resize completely when size of LV is already matching
and finaly at the most recent resize changeset for resize the
check for matching size has been eliminated as well so we ended
with a request call to resize fs to 0 size in some cases.

This commit reoders some test so the prompt happens just once before
resize of possibly 2 related volumes.

Also extra test for having LV already given size is added, and
whole metadata update is skipped for this case as the only
result would be an increment of seqno.

However the filesystem is still resized when requested,
so if the LV has some size and the resize is resolved to
the same size, the filesystem resize is called so in case FS
would not match, the resize will happen.