AllKeys() now includes bound flag and env var keys
AllKeys() now includes bound flag and env var keys

This patch fixes a bug where the function `AllKeys()` did not include
the keys for bound flags and environment variables.

samt42/viper,ishidawataru/viper,spf13/viper,vasu1124/viper,istio/viper,akutz/viper,dvln/viper