The linter found staticcheck and errorcheck issues. Deferred statements now use join to combine any new error with an existing one, preventing error information from being lost. Other minor error checks, like for printing text and flushing data have also been addressed.
This doesn't really matter because `ignition-validate` takes no flag
other than the special `-version` flag, but if it did (or it one day
does), one would quickly realize that `os.Args[1:]` is wrong and that
one instead wants `flag.Args()`, which are the args that aren't flags.
Historically, a spec version's Parse() has called the prior version's
parser if the config version is unrecognized. That is no longer the case,
so since ignition-validate calls the 3.0 parser, it will only accept 3.0
configs. Call the version-independent Parse() wrapper instead.
Bumps the import path to be `github.com/coreos/ignition/v2`, this is
required to be able to import the v2 of Ignition alongside v0 in other
repositories.
