SQL Server Role to View Job Logs

I had the same exact problem - I had a new user which wanted to add jobs. I added this user to msdb db and added him to sqlAgentOperatorRole and db_datareader, db_datawriter. Still, when trying to add a new job, the user was getting the same error:

Cannot execute as the database principal because the principal "guest" does not exist, this type of principal cannot be impersonated, or you do not have permission. (Microsoft Server, Error: 15517)

I traced it down and it looks like when trying to add a new job (or doing many other things...) the following query is run:

exec master.dbo.sp_Msdbuserpriv 'serv'

So, obviously I had to add the new user to Master as well:

use master
create user [youNewUser] for login [yourNewUserLogin]
alter user [youNewUser] with default_schema=[dbo]

And now it works like charm...

I am not sure of any other alternative but i believe user needs to be there in MSDB or should have the admin rights to execute or perform any required action on the job. There is a connect item about this as well, SQL2005 SQLAgent MSDB security roles

Or you can use an option as mentioned here:

You could create a stored procedure that runs the job. You can use with execute as owner to run the stored procedure as the database owner. That way, the users themselves don't need permissons on sp_start_job

Also, if feasible, you can read Launching SQL Agent Job from stored procedure not on [msdb] database, or, How Necessary is SET TRUSTWORTHY ON?