CBQE-2431: Move `test_view_startkey_endkey_validation` test

The test_view_startkey_endkey_validation` test is the only test that
is actually run from the `viewtests.py` file. This test is now moved
into the `ViewMergingTests` class. This makes the `viewtests.py` file
obsolete.

Change-Id: Ib11ec19f293bc1ae5bffe143ca7f6fa78069b415
Reviewed-on: http://review.couchbase.org/42134
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>