avocado.core.sysinfo log when sysinfo files are not present

Currently we fail silently when sysinfo configuration files
are not present. This patch adds a log.debug message so the user
will have a chance to understand why sysinfo is not being
collected.

Reference: https://trello.com/c/5rvvdH8lSigned-off-by: NAmador Pahim <apahim@redhat.com>

avocado/core/sysinfo.py

@@ -335,15 +335,24 @@ class SysInfo(object):
                                            'commands',
                                            key_type='str',
                                            default='')
+
+        if os.path.isfile(commands_file):
             log.info('Commands configured by file: %s', commands_file)
             self.commands = genio.read_all_lines(commands_file)
+        else:
+            log.debug('File %s does not exist.', commands_file)
+            self.commands = []
 
         files_file = settings.get_value('sysinfo.collectibles',
                                         'files',
                                         key_type='str',
                                         default='')
+        if os.path.isfile(files_file):
             log.info('Files configured by file: %s', files_file)
             self.files = genio.read_all_lines(files_file)
+        else:
+            log.debug('File %s does not exist.', files_file)
+            self.files = []
 
         if profiler is None:
             self.profiler = settings.get_value('sysinfo.collect',
@@ -357,10 +366,9 @@ class SysInfo(object):
                                            'profilers',
                                            key_type='str',
                                            default='')
+        if os.path.isfile(profiler_file):
             self.profilers = genio.read_all_lines(profiler_file)
-
             log.info('Profilers configured by file: %s', profiler_file)
-        log.info('Profilers declared: %s', self.profilers)
             if not self.profilers:
                 self.profiler = False
 
@@ -369,6 +377,9 @@ class SysInfo(object):
                     log.info('Profiler disabled: no profiler commands configured')
                 else:
                     log.info('Profiler disabled')
+        else:
+            log.debug('File %s does not exist.', profiler_file)
+            self.profilers = []
 
         self.start_job_collectibles = set()
         self.end_job_collectibles = set()