20969: Reloads nginx when custom TLS cert and key files change.

20969: Reloads nginx when custom TLS cert and key files change.

The way it's implemented may appear overly complicated, but we do the extra
check to avoid restarting nginx with a crt file that doesn't correspond to
the key file. This will happen otherwise, as 'cmd.run' will get executed on
any of the files listed inside 'onchanges'.

Arvados-DCO-1.1-Signed-off-by: Lucas Di Pentima <lucas.dipentima@curii.com>