Delete the reachability tests

Delete the reachability tests

It removes 001__reachability.robot as it is now part of OpenDaylight
integration/test. It completes the commit which pushes upstream the
reachability tests [1].

[1] https://git.opendaylight.org/gerrit/#/c/46910/

Conflicts:
      testcases/Controllers/ODL/OpenDaylightTesting.py
      unit_tests/odl/test_odl.py

Change-Id: I72926cd4ab77e12ba4aeabf03bdd35619d43ffd3
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
(cherry picked from commit d3042a7aa885d7761289661fb728f4d7b5e7c94b)