observe_t: check for lcb >= 2.3.0 for observe-master-only

This feature is not available on older lcb versions

Change-Id: I06a468f71503ce350edbb94c5d4240f428dd1c3c
Reviewed-on: http://review.couchbase.org/37078
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Volker Mische <volker.mische@gmail.com>

couchbase/tests/cases/observe_t.py

@@ -78,6 +78,7 @@ def test_multi_observe(self):
 
 class ConnectionObserveMasterTest(MockTestCase):
     def test_master_observe(self):
+        self.skipLcbMin("2.3.0")
         key = self.gen_key("test_master_observe")
         rv = self.cb.set(key, "value")
         obs_all = self.cb.observe(key)