Werk #11508: Fix error when editing host configuration

Component	Setup
Title	Fix error when editing host configuration
Date	Oct 29, 2020
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	2.0.0b1 Checkmk MSP (CME)

When editing the CME configuration while having folders with explicit site configurations, an error like this occured in 2.0.0i1: "FileExistsError ((17, 'File exists'))"

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