log: log command executed on LogCmd errors.
log: log command executed on LogCmd errors.

Some call sites are doing this ad-hoc inconsistently, just always log
this when there's an error, with the error, full command line, stdout,
and stderr nicely ordered.

dgonyeo/ignition,AlexNPavel/ignition,ajeddeloh/ignition,dgonyeo/ignition,AlexNPavel/ignition,coreos/ignition,coreos/ignition,higebu/ignition,higebu/ignition,ajeddeloh/ignition,AlexNPavel/ignition,dgonyeo/ignition,coreos/ignition,higebu/ignition,ajeddeloh/ignition