FIX: infinite recursion in TronGrid client

[mbalashovv]

There was infinite recursion in HTTP provider because of condition

if len(self._api_keys) > 1:

not making self._api_keys list be empty. That's why random.choice(self._api_keys) always had elements to get for making requests

@andelf

[MrNaif2018]

Hi, why did you close the PR?

[mbalashovv]

My mistake. I reopened it

[mbalashovv]

Please consider to look at this
@andelf @MrNaif2018

[andelf]

Looks good. Better use another error type.

[mbalashovv]

We can use the existing UnknownError or create a new error something like CredentialsError, which can be used for API services but not for nodes