Fix pylint warnings in test_testcase_base
Fix pylint warnings in test_testcase_base

It takes into account the following warnings:
  - wrong-import-order
  - no-value-for-parameter

The 'no-value-for-parameter' warnings are false positive. The added
default values are useless but avoid them.

Change-Id: I50d0af178d9da668a3c72e75f5af467d36ca0e6a
Signed-off-by: Cédric Ollivier <d48310251a4a484d041bc5d09a9ac4d86d20f793@orange.com>

opnfv/functest,mywulin/functest,opnfv/functest,mywulin/functest