[contrail] no requirements for the junos-eznc package installation

[Ruslan Khozinov]

The "junos-eznc" package is used for contrail tests. But plugin tests has no requirements for that package.

Traceback (most recent call last):
  File "/home/jenkins/workspace/9.1.contrail.5.0.bvt.test.juniper/plugin_test/run_tests.py", line 78, in <module>
    import_tests()
  File "/home/jenkins/workspace/9.1.contrail.5.0.bvt.test.juniper/plugin_test/run_tests.py", line 54, in import_tests
    from tests import test_smoke_bvt # noqa
  File "/home/jenkins/workspace/9.1.contrail.5.0.bvt.test.juniper/plugin_test/tests/test_smoke_bvt.py", line 30, in <module>
    from helpers import vsrx
  File "/home/jenkins/workspace/9.1.contrail.5.0.bvt.test.juniper/plugin_test/helpers/vsrx.py", line 20, in <module>
    from jnpr.junos import Device
ImportError: No module named jnpr.junos