detect: Don't add empty lists

If we don't have any areca controller, areca.detect() return an empty list.
It was then added to hrdw by an append.

This commit does :
- return None instead of an empty list if no controller got detected
- filter-out all None items out of the hdrw list
- makes a one liner to append areca into hrdw

Signed-off-by: Erwan Velu <e.velu@criteo.com>

hardware/areca.py

@@ -190,4 +190,9 @@ def detect():
             hwlist.append(('areca', "disk%d" % disk_number, info,
                            disk_info_out[info]))
 
-    return hwlist
+    if len(hwlist):
+        return hwlist
+
+    # If we dont't detect any areca controller, return None
+    # This avoid having empty lists
+    return None

hardware/detect.py

@@ -927,8 +927,7 @@ def main():
     args = parse_args(sys.argv[1:])
 
     hrdw = []
-    areca_hrdw = areca.detect()
-    hrdw.append(areca_hrdw)
+    hrdw.append(areca.detect())
     detect_hpa(hrdw)
     detect_megacli(hrdw)
     detect_disks(hrdw)
@@ -955,6 +954,8 @@ def main():
 
     hrdw = clean_tuples(hrdw)
 
+    hrdw = list(filter(None, hrdw))
+
     if args.human:
         pprint.pprint(hrdw)
     else: