s3_upgrade: Update commandline options and use updated samba3 python module

s3_upgrade: Update commandline options and use updated samba3 python module

upgrade_from_s3 script now requires samba3 configuration file and target
directory for samba4 database. In addition, it either uses --libdir option
or --testparm option to correctly guess the paths for samba3 databases
(private dir and state directory).

Usage: upgrade_from_s3 [options] <configuration_file> <targetdir>

Input arguments are:
  <configuration_file> - path to existing smb.conf
  <targetdir>          - directory in which samba4 database will be created

In addition, specify either samba3 database directory (with --libdir) or
samba3 testparm utility (with --testparm).

Before using passdb interface, initialize s3 loadparm context using
correct path settings for private dir and state directory.

Export account policy from s3 to s4.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>