Fix pylint warnings in testcase_base
Fix pylint warnings in testcase_base

It takes into account the following warnings:
  - bare-except
  - unused-argument
  - broad-except

Change-Id: I3a50bf6d07823edc80a7f0f78f46681ace7f4a39
Signed-off-by: Cédric Ollivier <d48310251a4a484d041bc5d09a9ac4d86d20f793@orange.com>

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