s3:popt_common: use cmdline_messaging_context() in popt_common_credentials_callback()

s3:popt_common: use cmdline_messaging_context() in popt_common_credentials_callback()

This adds a call to cmdline_messaging_context() to the popt
popt_common_credentials_callback() hook and ensures that any client tool
that uses POPT_COMMON_CREDENTIALS gets an implicit messaging context,
ensuring it doesn't crash in the subsequent lp_load_client() with
include=registry in a cluster.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13465

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Christof Schmitt <cs@samba.org>