VPP-1495: Fix intermittent stat sock test failures.

VPP-1495: Fix intermittent stat sock test failures.

Loosen polling loop while waiting for stats socket.

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Classifier IP6 UDP proto Test Case
==============================================================================
connect: No such file or directory
==============================================================================
ERROR: setUpClass (test_ip4.TestIPLoadBalance)
------------------------------------------------------------------------------
Traceback (most recent call last):
  File "/vpp/test/framework.py", line 424, in setUpClass
    cls.statistics = VPPStats(socketname=cls.stats_sock)
  File "build/bdist.linux-x86_64/egg/vpp_papi/vpp_stats.py", line 120, in _init_
    raise IOError()
IOError

Change-Id: I80523122f96eafc41b3ebbf27bee73f6c637d781
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>