app-admin/collectd: Bumped to v5.5.1

app-admin/collectd: Bumped to v5.5.1

- New upstream version (Closes #570766, #517060)

- Bumped to EAPI=6

- Non-functional mongodb plugin disabled in ebuild (see upstream
  issue #492, closes #524400)

- Multiple dependency problems fixed

- linux-info eclass usage fixed (Closes #570778)

- Support for new plugins added (amqp, genericjmx, ipvs, modbus, sigrok,
  tail_csv, vserver, write_riemann)

- PYTHON_SINGLE_TARGET support for Python 3.4 and 3.5 enabled

- Documentation improved (USE flag description, elogs)

- Linux capabilities usage expanded to improve running collectd as
  unprivileged user (disable via filecaps USE flag)

- Runscript rewritten

  - Runscript now supports OpenRC's default status function

  - Runscript now guarantees service shutdown

  - Validating configuration before (re)starting daemon