Generate PubKey from SecKey if only SecKey is set in Visor config

[nkryuchkov]

Did you run make format && make check? Yes

Fixes #255

Depends on https://github.com/SkycoinPro/skywire-services/pull/128

Changes:

• Generate PubKey from SecKey if only SecKey is set in Visor config
• Change static_secret_key to secret_key in Visor JSON config.
• Change static_public_key to public_key in Visor JSON config.
• If a necessary config field is not set and default config value is generated, then the value is updated in the JSON config.

How to test this PR:

• Run generic integration env and check if Visor PK is generated correctly for the following conditions:
  • If both PK and SK are set in config, PK from config should be shown.
  • If only SK is set in config, the same PK should be shown.
  • If only PK is set in config, a newly generated PK should be shown.
  • If no keys are set in config, a newly generated PK should be shown.

[jdknives]

Should the PubKey be added to the config itself when it is generated? @nkryuchkov

[jdknives]

Also, when the secret key is empty and public key is empty, I get the following error:

FATAL [skywire]: Failed to decode &{%!s(*os.file=&{{{0 0 0} 7 {0} <nil> 0 1 true true true} /Users/rudikleine/go/src/github.com/SkycoinProject/skywire-mainnet/skywire-config.json <nil> false false false})}: Invalid secret key length

Config looks like this:

	"key_pair": {
		"static_public_key": "",
		"static_secret_key": ""
	}

[nkryuchkov]

@jdknives

Should the PubKey be added to the config itself when it is generated?

Yes, because if it is not set, it will be generated from SecKey next time Keys() is called. Also, cipher.GenerateKeyPair() generates both keys, so I think it's better to fill both at one time.

[nkryuchkov]

@jdknives

Also, when the secret key is empty and public key is empty, I get the following error:

In this case, keys are considered malformed, because the key_pair section is present in the config. However, I think it might be a good idea to generate new keys if they are malformed.