Werk #10377: Fix terminating "cmk --update-dns-cache" with CTRL+C

Component	Core & setup
Title	Fix terminating "cmk --update-dns-cache" with CTRL+C
Date	Oct 31, 2019
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	2.0.0i1 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME) 1.6.0p6 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME)

Previously the CTRL+C termination was not working during the whole execution time of the call.

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