stack/erp5/WCFS+NEO{SSL:1}: Auto-deploy SSL files from instance parameters

Before this patch SlapOS users had to manually add SSL files in case WCFS
was used in combination with NEO+SSL. This is bad as we can easily forget
to update local parameter files when updating instance parameters ("_ca",
"_cert" and "_key"). This builds up on 706801f2.

/reviewed-by @kirr @jerome
/reviewed-on !1620