Fix a problem that uses an error object after it is freed.
Remove a word: 'Failed' in an error message.

The error message of a GError class includes the meaning of failed
like the following example. So it is redundant.

[ERR] <ActionManager.cc:772> Failed: Failed to execute child process "makan-kosappo" (No such file or directory), action ID: 1, log ID: 51235, server ID: 1, event ID: 2421, time: 1379302041.212157655, type: Activated, trigger ID: 13498, status: Invalid: 2, severity: CRITICAL, host ID: 10084