r23859: Work to have Group Policy work 'out of the box' in Samba4.

r23859: Work to have Group Policy work 'out of the box' in Samba4.

This involves creating the SYSVOL and NETLOGON shares at provision
time, and creating the right subdirectories.

This also changes the behaviour of lp.get("foo") in ejs - we now
return undefined, rather than syntax error, if the parameter doesn't
exist (perhaps because the share isn't defined).

Andrew Bartlett
(This used to be commit 45cadf3bc0d38f6600666511a392e1ce353adee7)