And not only for the content of params, assuming the existence of
params.  This fixes the following error:

   $ avocado run passtest.py --vm-domain f26 --vm-username root
   JOB ID     : 488c8f26de7b52707e8ddb2b89d0f03a0622391d
   JOB LOG    : /home/cleber/avocado/job-results/job-2018-03-26T16.58-488c8f2/job.log
   DOMAIN     : f26
   LOGIN      : root@f26 (TIMEOUT: 120 seconds)
    (1/1) passtest.py:PassTest.test: PASS (0.01 s)
   RESULTS    : PASS 1 | ERROR 0 | FAIL 0 | SKIP 0 | WARN 0 | INTERRUPT 0 | CANCEL 0
   JOB TIME   : 1.39 s
   Error running method "render" of plugin "html": 'params'
Signed-off-by: NCleber Rosa <crosa@redhat.com>