Fix version check to enable streaming keep-alive

Error Message

Expected [['COMPLETED']] from SELECT bootstrapped FROM system.local WHERE key='local', but got [[u'IN_PROGRESS']]
-------------------- >> begin captured logging << --------------------
dtest: DEBUG: cluster ccm directory: /tmp/dtest-YmnyEI
dtest: DEBUG: Done setting configuration options:
{   'num_tokens': None, 'phi_convict_threshold': 5, 'start_rpc': 'true'}
cassandra.cluster: INFO: New Cassandra host <Host: 127.0.0.1 datacenter1> discovered
--------------------- >> end captured logging << ---------------------
Stacktrace

  File "/usr/lib/python2.7/unittest/case.py", line 329, in run
    testMethod()
  File "/home/automaton/cassandra-dtest/tools/decorators.py", line 46, in wrapped
    f(obj)
  File "/home/automaton/cassandra-dtest/bootstrap_test.py", line 163, in simple_bootstrap_test_small_keepalive_period
    assert_bootstrap_state(self, node2, 'COMPLETED')
  File "/home/automaton/cassandra-dtest/tools/assertions.py", line 297, in assert_bootstrap_state
    assert_one(session, "SELECT bootstrapped FROM system.local WHERE key='local'", [expected_bootstrap_state])
  File "/home/automaton/cassandra-dtest/tools/assertions.py", line 130, in assert_one
    assert list_res == [expected], "Expected {} from {}, but got {}".format([expected], query, list_res)
"Expected [['COMPLETED']] from SELECT bootstrapped FROM system.local WHERE key='local', but got [[u'IN_PROGRESS']]\n-------------------- >> begin captured logging << --------------------\ndtest: DEBUG: cluster ccm directory: /tmp/dtest-YmnyEI\ndtest: DEBUG: Done setting configuration options:\n{   'num_tokens': None, 'phi_convict_threshold': 5, 'start_rpc': 'true'}\ncassandra.cluster: INFO: New Cassandra host <Host: 127.0.0.1 datacenter1> discovered\n--------------------- >> end captured logging << ---------------------"