Optimize code (tasks list initialization, task verification)

Signed-off-by: Przemek Stekiel <przemyslaw.stekiel@mobica.com>
diff --git a/tests/scripts/analyze_outcomes.py b/tests/scripts/analyze_outcomes.py
index 2cdad69..ba38ec2 100755
--- a/tests/scripts/analyze_outcomes.py
+++ b/tests/scripts/analyze_outcomes.py
@@ -175,17 +175,15 @@
 
         result = True
 
-        tasks = []
         if options.task == 'all':
-            for task in TASKS:
-                tasks.append(task)
+            tasks = TASKS.keys()
         else:
             tasks = options.task.split(',')
 
-        for task in tasks:
-            if task not in TASKS:
-                print('Error: invalid task: {}'.format(task))
-                sys.exit(1)
+            for task in tasks:
+                if task not in TASKS:
+                    print('Error: invalid task: {}'.format(task))
+                    sys.exit(1)
 
         for task in TASKS:
             if task in tasks: