Added smbc_SetConfiguration which lets the user set the smb.conf for libsmbclient code

[github at samba.org]

New comment by puran157 on Samba Github repository

https://github.com/samba-team/samba/pull/113#issuecomment-349645214
Comment:
About torture tests, I was thinking to have a temporary smb.conf with modified configuration and use that to update configuration, verify if configuration is reflected or not, undo that with that of default smb.conf and verify if configuration is undone or not. 

I just don't know where to put that smb.conf and which smb.conf should be used to restore configuration. (Restoring configuration is important because we don't want other torture tests to get impacted)

Any suggestion in this regard would be great.