ctdb-scripts: Ignore shellcheck SC2181 warning (use of $?)

ctdb-scripts: Ignore shellcheck SC2181 warning (use of $?)

Given the size of the command substitutions it would be less clear to
embed the assignments and substitutions inside a conditional.  It is
clearer if the exit code is checked afterwards.

However, do fix some untidy uses of != instead of -ne when comparing
with $?.  Make the code easier to understand by reversing the logic
and using -eq and ||.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>