Lazy import is not needed

There was an abandoned change that made reference to a RecussionError
when running a probe test that imported boto3 that had something to do
with eventlet, ssl and a transitive dependency on requests-mock, but the
fix that actually got merged seemed to depend on another change to
tox.ini that disables request-mock when we run pytest.

Either way, we already import from boto3 at the top of probe tests and
it's in test-requirements; so we require it to be installed even if you
don't have s3api in your pipeline.

Related-Change: I789b257635c031ac0cb6e4b5980f741e0cb5244d
Related-Change: I2793e335a08ad373c49cbbe6759d4e97cc420867
Related-Change: If14e4d2c1af2efcbc99e9b6fe10973a7eb94d589

Change-Id: Id2662bfc5ef2f21f901f1c98e6389c4cb01818a2

test/probe/test_mixed_policy_mpu.py

@@ -26,6 +26,7 @@ from test.probe.brain import BrainSplitter
 from test.probe.common import ReplProbeTest, ENABLED_POLICIES
 
 from boto3.s3.transfer import TransferConfig
+from test.s3api import get_s3_client
 
 import mock
 
@@ -40,8 +41,6 @@ class TestMixedPolicyMPU(ReplProbeTest):
         if not s3api_info:
             raise unittest.SkipTest('s3api not enabled')
 
-        # lazy import boto only required if cluster supports s3api
-        from test.s3api import get_s3_client
         self.s3 = get_s3_client(1)
 
         self.bucket_name = 'bucket-%s' % uuid.uuid4()