Add --json option to get balance as JSON

[sculptex]

usd - Current USD value,
zcn - ZCN amount (float)
fmt - Formatted zcn value (mZCN etc.)

A brief description of the changes in this PR:

Tasks to complete before merging PR:

• Ensure system tests are passing. If not Run them manually to check for any regressions 📋
• Do any new system tests need added to test this change? do any existing system tests need updated? If so create a PR at 0chain/system_test
• Merge your system tests PR to master AFTER merging this PR

Associated PRs (Link as appropriate):

• blobber:
• gosdk:
• system_test:
• zboxcli:
• 0chain:
• Other: ...

[sculptex]

Actually, for true JSON support for such commands, we could have a success variable. Only when success:true would the user then read the rest of the values. An alternative would be just to return relevant parameters of ZCN being 0.

For now, I will just class invalid JSON as 0.

[peterlimg]

Check error in case use invalid value is used

[sculptex]

--json is bool so requires no parameter. But feel free to change however is best way

[sculptex]

@peterlimg do you agree? there is no parameter to check?

[sculptex]

@peterlimg what is your opinion on having success field?
So that with --json, valid json is always returned, even if just {"success"=false} or whatever.
But then client only checks other values if success=true?

[peterlimg]

@peterlimg what is your opinion on having success field? So that with --json, valid json is always returned, even if just {"success"=false} or whatever. But then client only checks other values if success=true?

I would suggest to not add the success field, we can return json value when success, and return error directly. We can put the command in RunE(), so when error happens, it will have a formatted message returned, i.e, "Error: xxxx", so if the CLI is used by other services, the prefix of "Error" could be checked.

[sculptex]

Okay, sure.

[sculptex]

@peterlimg sorry, I'm not too hot with GitHub, am I required to implement your changes before you can approve and close?

[sculptex]

@peterlimg can this be merged now?

[cnlangzi]

LGTM

[sculptex]

why wasn't this merged? now its conflicting again..

fixed