agent/samba4: Relax requirement for smb.conf file to exist to activate the module
agent/samba4: implement samba4 option value getters
agent/samba4: implement isSamba4Provisioned() and getSamba4GlobalInfo() calls

getSamba4GlobalInfo() is primary to get us desired options
from [global] section in smb.conf
We could use those to make a "Samba4/domain info" type of page
agent/samba4: Don't use Bind as DNS backend on pristing MBS installation

I think using internal DNS implementation is going to bootstrap us faster
agent/samba4: Load Samba4 configuration during samba4 module initialization
web/samba4: XMLRPC proxies for isSamba4Provisioned() and getSamba4GlobalInfo()