puppeth: handle encrypted ssh keys (closes #15442) (#15443)

* cmd/puppeth: handle encrypted ssh keys

* cmd/puppeth: fix unconvert linter error

vendor/golang.org/x/sys/unix/mksysnum_darwin.pl

@@ -16,7 +16,7 @@ my $command = "mksysnum_darwin.pl " . join(' ', @ARGV);
 
 print <<EOF;
 // $command
-// MACHINE GENERATED BY THE ABOVE COMMAND; DO NOT EDIT
+// Code generated by the command above; see README.md. DO NOT EDIT.
 
 // +build $ENV{'GOARCH'},$ENV{'GOOS'}