net/py-lib389: Fix instance creation on FreeBSD

Adjust the FreeBSD patch for lib389's instance setup code.

Guard the container detection against a missing systemd-detect-virt
binary. Upstream initializes container_result to an integer and then
unconditionally executes systemd-detect-virt on non-containerised
systems, which aborts instance creation with a FileNotFoundError on
FreeBSD. The check now only runs when the binary is present and
falls back to the non-container code path otherwise.

Use a plain localhost LDAP connection with the generated temporary
Directory Manager password for the authenticated setup session, as
LDAPI autobind via SASL EXTERNAL did not work reliably during setup
on FreeBSD.

Sponsored by: Netzkommune GmbH