Werk #7962: Fix various bugs in the liebert* check plugins

Component	Checks & agents
Title	Fix various bugs in the liebert* check plugins
Date	Aug 1, 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) 1.6.0b5 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME) 1.5.0p22 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME)

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