fixed imports in db_pool_test, timer_test and tpool_test

greentest/db_pool_test.py

@@ -24,7 +24,8 @@
 
 import os.path
 
-from eventlet import api, coros, tests
+from eventlet import api, coros
+from greentest import tests
 from eventlet import db_pool
 
 class DBTester(object):

greentest/timer_test.py

@@ -24,7 +24,8 @@ THE SOFTWARE.
 
 import unittest
 
-from eventlet import api, tests, timer
+from eventlet import api, timer
+from greentest import tests
 
 class TestTimer(tests.TestCase):
     mode = 'static'

greentest/tpool_test.py

@@ -17,10 +17,10 @@ See the License for the specific language governing permissions and
 limitations under the License.
 """
 
-import os, socket, time, threading
-from eventlet import coros, api,  tpool, tests
+import time
+from eventlet import coros, api,  tpool
+from greentest import tests
 
-from eventlet.tpool import erpc
 from sys import stdout
 
 import random