avocado.core.job: Print on log errors loading plugins

In certain situations where avocado might be running
headless, we still want users to know of errors loading
plugins. So output problems into the main job log.
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>

avocado/core/job.py

@@ -43,6 +43,9 @@ from avocado.utils import archive
 from avocado.utils import path
 from avocado.settings import settings
 
+from avocado.core.plugins.builtin import ErrorsLoading
+
+
 try:
     from avocado.core.plugins import htmlresult
     HTML_REPORT_SUPPORT = True
@@ -320,6 +323,11 @@ class Job(object):
         self.view.start_file_logging(self.logfile,
                                      self.loglevel,
                                      self.unique_id)
+
+        for plugin_failed in ErrorsLoading:
+            _TEST_LOGGER.error('Error loading %s -> %s' % plugin_failed)
+        _TEST_LOGGER.error('')
+
         _TEST_LOGGER.info('Job ID: %s', self.unique_id)
         _TEST_LOGGER.info('')