Make Samba4 pass the NET-API-BECOMEDC test against Win2k3 (again).

Make Samba4 pass the NET-API-BECOMEDC test against Win2k3 (again).

To make Samba4, using the python provision system, pass this test
required some major rework.  Untested code is broken code, and some of
the refactoring for a seperate provision test (which also now passes)
broke things.

Similarly, the iconv work has compiled, but these codepaths have never
been run (NULL pointer de-reference).

In working to use a local, rather than global, loadparm context, and
to support using a target directory, a few things needed to be
reworked, particularly around path handling.

Andrew Bartlett
(This used to be commit 1169e8d7bee20477b0efbfea3534ac63c83fb3d6)