Title: It seems command line option --v2-config-only has wrong default value

I cannot start ./envoy-static with v1 config, but it works when start ./envoy-static with command line --v2-config-only.

Then I opened the source file 'source/server/options_impl.cc' and found the code:

TCLAP::SwitchArg v2_config_only("", "v2-config-only", "parse config as v2 only", cmd, true);

I don't know why --v2-config-only default value is true, and negated when specified. It seems strange.