s4:torture/rpc/samr - enhance the "EnumDomainGroups" test regarding universal groups

s4:torture/rpc/samr - enhance the "EnumDomainGroups" test regarding universal groups

Find the "Enterprise Admins" group which does exist on s4 and Windows
directories and is always per default universal. Test this only when the target
is set to s4 (s3 deployments don't contain this group). If the number of
returned objects is "0" (count) then we are likely testing the builtin domain of
an AD deployment.Then we ignore the inexistent "Enterprise Admins" group.

I didn't enhance the test for "QueryDomainInfo" since this does itself a
comparison of all returned objects with the "EnumDomainGroups" call. Therefore
if the latter passes, and the "QueryDomainInfo" test passes also the
"QueryDomainInfo" call is okay regarding groups.