[MINOR] checks: ensure that we can inherit binary checks from the defaults section

[MINOR] checks: ensure that we can inherit binary checks from the defaults section

Health checks were all pure ASCII, but we're going to have to support some
binary checks (eg: SQL). When they're inherited from the default section,
they will be truncated to the first \0 due to strdup(). Let's fix that with
a simple malloc.
(cherry picked from commit 98fc04a766bcff80f57db2b1cd865c91761b131b)