vsh: Drop redundant definition searches from vshCmd{def,Grp}Help

vsh: Drop redundant definition searches from vshCmd{def,Grp}Help

These helpers are called from a single place only - cmdHelp wrapper and
just before the wrapper invokes the helpers, it performs the search,
either for command group or for the command itself, except the result is
discarded and the helper therefore needs to do it again. Drop this
inefficient handling and pass the @def structure rather than a name,
thus preventing the helper from needing to perform the search again.

Signed-off-by: Erik Skultety <eskultet@redhat.com>