ctdb-tools: "ctdb nodestatus" should only display header for "all"

ctdb-tools: "ctdb nodestatus" should only display header for "all"

The "Number of nodes:" header should only be displayed when "all" is
specified.  This is how the command behaved in Samba <= 4.4.

Printing the number of nodes is not helpful and is rather confusing in
the default case where only the status of the current node is printed.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12802

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
(cherry picked from commit 1d10c8e9e637619b754b4a273d3c714fbca7d503)