Integrate meta-seconorth-distro/postinstall-fngsystem

Commit: seco-ne/yocto/layers/meta-seconorth-distro@f9407345

shared-conf: Allow on/off for bool values not only true/false

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Commit: seco-ne/yocto/layers/meta-seconorth-distro@920b5c91

fnginstall-postinstallation: Fix boot partition detection for fngsystem

The scripts failed if run in an installed fngsystem. This is needed in FT2, when new xml files are installed after the FNGSystem installation.