Showing failed to take screenshot message if gauge_screenshot fails

Author: kashishm

getgauge/registry.py

@@ -139,6 +139,7 @@ def _take_screenshot():
     temp_file = os.path.join(tempfile.gettempdir(), 'screenshot.png')
     call(['gauge_screenshot', temp_file])
     if not os.path.exists(temp_file):
+        print("Failed to take screenshot using gauge_screenshot.")
         return str.encode("")
     _file = open(temp_file, 'r+b')
     data = _file.read()