Werk #13026: agent plugin mk_db2.linux: fix timeout

When the db2 queries take longer than 10 seconds, the command is terminated.

Before this fix the termination did not work out as expected: Only the currently running command was terminated, but the script was still running in the background. This lead to a very confusing output: The output of the terminated script was interleaved with the output of the remaining script. The sections where mixed up and various other db2 checks crashed with strange error messages.

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