rt: remove certificate verification

* Since inspirert.cern.ch certificate is invalid and in newer versions
  of the library used by rt it is enforced to be valid, modify rt
  to keep the old behaviour
installation: configurable task submitter

* In commit e2eb2863288fa7e14a36ced9323191abe38851a7, the task submitter
  was removed; it is however needed with upstream Invenio sources.  This
  commit makes the behaviour configurable.