Check return code on restore image command

When restore image command was sent and the restoration failed, you
could see in WebConsole the image as restored and the command completed,
as it if had not failed. This happened because ogClient did not check
the return code of restoration script.

This commit adds return code check on restore image. So, when return
code is a non-zero value ogClient responses with an error 500. When
ogServer receives this error response, it did not set in the database
the image as restored and command as completed without errors.

src/linux/ogOperations.py

@@ -195,6 +195,8 @@ class OgLinuxOperations:
                                shell=True,
                                executable=OG_SHELL)
             (output, error) = ogRest.proc.communicate()
+            if (ogRest.proc.returncode):
+                raise Exception
         except:
             raise ValueError('Error: Incorrect command value')