Avoid using LMDB environments across forks

Avoid using LMDB environments across forks

In krb5kdc and kadmind, reinitialize the DB state after daemonizing,
to prevent using an LMDB environment in a different process than it
was created.  Otherwise the daemon's reader table slot appears to be
stale and can be claimed by another process.

In kadmind, this change means that global_server_handle changes value
after the loop setup.  Add an extra level of pointer indirection so
that the handle passed to the loop remains valid.

kdb_init_hist() is now called twice by kadmind.  Change it to avoid
leaking hist_princ on the second invocation.

ticket: 8918
tags: pullup
target_version: 1.18-next
target_version: 1.17-next