Add additional test coverage for helper functions in Util

Currently helper functions in Util lacks test coverage

This commit adds test coverage for the following functions by addressing the review feedback
- GetConfigDirPath
- GetGrpcConnection
- SaveCredentials
- RemoveCredentials
- RefreshCredentials
- LoadCredentials
- RevokeToken
- GetJsonFromProto
- GetYamlFromProto
- TestOpenFileArg
- ExpandFileArgs
Signed-off-by: Kugamoorthy Gajananan <[email protected]>

Signed-off-by: Kugamoorthy Gajananan <[email protected]>

Author: gajananan