Fix deps for api-samples tox env

The api-samples tox target fails since it needs the
PlacementFixture which comes from the placement repo.
This fixes it by using the same deps trick as the other
functional test environments.

As a result, the shared environment is also removed.

Change-Id: I815b8b3cff5dcbb0fc4be5f1d85019111c2009e5

tox.ini

@@ -133,11 +133,11 @@ commands =
   {[testenv:functional]commands}
 
 [testenv:api-samples]
-envdir = {toxworkdir}/shared
 setenv =
   {[testenv]setenv}
   GENERATE_SAMPLES=True
   PYTHONHASHSEED=0
+deps = {[testenv:functional]deps}
 commands =
   {[testenv]commands}
   stestr --test-path=./nova/tests/functional/api_sample_tests run {posargs}