mgr/smb: generate smb.conf hosts allow & hosts deny values

mgr/smb: generate smb.conf hosts allow & hosts deny values

Using the Share resource hosts_access parameter generate
smb.conf-equivalent configuration for the 'hosts allow' and 'hosts deny'
configuration parms. Note that currently we automatically set hosts deny
to all if *any* hosts allow is set to avoid the possibly surprising
result of explicitly setting hosts to allow and then having the share
continue to allow hosts not explicitly listed.

If needed, in the future we could allow the user to override the
default deny - but I'm trying to keep it real simple for now.

Signed-off-by: John Mulligan <jmulligan@redhat.com>