netconfig: improved troubleshooting capabilities

Added NETCONFIG_VERBOSE and NETCONFIG_FORCE_REPLACE config
variables allowing to run all netconfig calls in debug mode
and force update of modified files as default. Show service,
policy resolving info and log the commandline in debug mode.
Fixed to log info/warnings that were printed to stderr only
before (bnc#860644, bnc#868323).
ifup: startmode ifplugd logic error regression fix

Fixed a logic error regression breaking startmode ifplugd
introduced while fixing bnc#846361 (bnc#869761,bnc#866870)
updated changes (obs maintenance request #228168)