Empty (commented out) config file rejected

[farshidtz]

A fully or partially commented out config file should be accepted. Top level keys must not be mandatory.

An empty config file is currently rejected and there are tests for that:

rt-conf/cmd/rt-conf/main_test.go

Lines 68 to 70 in 1ce23b4

	err: "failed to load config file: empty config file",
	yaml: `
	# Kernel command line parameters

Some other tests add keys to work around this issue.