Where is the default location for the SQL Agent Job step output file? How do I update it? I recently migrated my system databases to a new location.

I then experienced failures of my SQL Agent jobs with the following error:

2015-10-03 01:53:10 - ! [136] Job  -     reported: Unable to open Step output file.


I can set the location for the step output file by accessing the 'Job Step Properties - Advanced' tab, but it is blank.  

Where is the default location for this?

I have found resources which specify it is 
The default location depends on the location of your 

C:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\Log\xxxxx.txt 

but this is not the case on my server.  Is there an environment variable that holds the path to MSSQL\Log as I changed the directory and this would explain why the failures occurred.  I would like to update the default without having to enter a static location for every job.

I initially thought this could be set by using the sp_set_sqlagent_properties store procedure like so:

USE MASTER
GO
EXEC msdb.dbo.sp_set_sqlagent_properties 
@errorlog_file=N'U:\Microsoft SQL Server\MSSQL.1\MSSQL\LOG\SQLAGENT.OUT'
GO


But this still allows existing jobs to fail.

Is there a way to script the update of the step file location from one drive to another but using the same file paths and names?
If the Job Step runs a Maintenance Plan, then the logging is perhaps being done in the "Maintenance Plan" which is somewhat common. Choose the specific Maintenance Plan (from SSMS -> Management -> Maintenance Plans) that is referenced by the Agent Job, click on the circled icon for "Reporting and Logging" and check the logging location on it as shown in the dialog below: