Reduce redundant code

Signed-off-by: TTz0601 <1375888477@qq.com>

avocado/utils/softwareraid.py

@@ -48,10 +48,7 @@ def __init__(self, name, level, disks, metadata, spare_disks=None):
         self.metadata = metadata
         self.disks = disks
         self.remadd = ""
-        if not spare_disks:
-            self.spare_disks = []
-        else:
-            self.spare_disks = spare_disks
+        self.spare_disks = spare_disks or []
 
     def _run_command(self, cmd, log_details=True, check_recovery=False):
         if process.system(cmd, ignore_status=True, shell=True) != 0:
@@ -181,4 +178,4 @@ def exists(self):
         result = process.run(cmd, shell=True, sudo=True, ignore_status=True)
         if result.exit_status == 4:
             return False
-        return True
+        return True