sysinfo: include journalctl diff information

We have a LogWatcher class for system log files, but so far systemd
journal messages were ignored. This patch creates a jounalctl watcher
class and collects the journalctl messages diff per test, creating a gz
file out of them.
Signed-off-by: NAmador Pahim <apahim@redhat.com>

avocado/core/sysinfo.py

@@ -13,6 +13,7 @@
 # Author: John Admanski <jadmanski@google.com>
 
 import gzip
+import json
 import logging
 import os
 import shutil
@@ -213,6 +214,45 @@ class Daemon(Command):
         return retcode
 
 
+class JournalctlWatcher(Collectible):
+
+    """
+    Track the content of systemd journal into a compressed file.
+
+    :param logf: Basename of the file where output is logged (optional).
+    """
+
+    def __init__(self, logf=None):
+        if not logf:
+            logf = 'journalctl.gz'
+
+        super(JournalctlWatcher, self).__init__(logf)
+        self.cursor = self._get_cursor()
+
+    def _get_cursor(self):
+        try:
+            cmd = 'journalctl --lines 1 --output json'
+            result = process.system_output(cmd, verbose=False)
+            last_record = json.loads(result)
+            return last_record['__CURSOR']
+        except Exception as e:
+            log.debug("Journalctl collection failed: %s", e)
+
+    def run(self, logdir):
+        if self.cursor:
+            try:
+                cmd = 'journalctl --quiet --after-cursor %s' % self.cursor
+                log_diff = process.system_output(cmd, verbose=False)
+                dstpath = os.path.join(logdir, self.logf)
+                with gzip.GzipFile(dstpath, "w")as out_journalctl:
+                    out_journalctl.write(log_diff)
+            except IOError:
+                log.debug("Not logging journalctl (lack of permissions)",
+                          dstpath)
+            except Exception as e:
+                log.debug("Journalctl collection failed: %s", e)
+
+
 class LogWatcher(Collectible):
 
     """
@@ -442,6 +482,8 @@ class SysInfo(object):
         except ValueError as details:
             log.info(details)
 
+        self.end_test_collectibles.add(JournalctlWatcher())
+
     def _get_collectibles(self, hook):
         collectibles = self.hook_mapping.get(hook)
         if collectibles is None:

selftests/unit/test_sysinfo.py

@@ -85,8 +85,8 @@ class SysinfoTest(unittest.TestCase):
         job_postdir = os.path.join(testdir, 'post')
         self.assertTrue(os.path.isdir(job_postdir))
         # By default, there are no post test files
-        self.assertLess(len(os.listdir(job_postdir)), 2,
-                        "Post dir can contain 0-1 files depending on whether "
+        self.assertLess(len(os.listdir(job_postdir)), 3,
+                        "Post dir can contain 0-2 files depending on whether "
                         "sys messages are obtainable or not:\n%s"
                         % os.listdir(job_postdir))