s4:provision Allow provision-backend to not run slapd for 'make test'

s4:provision Allow provision-backend to not run slapd for 'make test'

As the version of OpenLDAP required for Samba4 is fairly new, we don't
want to make it a requirement before this python code is run in 'make
test'.

As such, skip over the actual starting of slapd, but check the rest
runs alright (which still validates syntax and other modules).

Andrew Bartlett