ndb_redis: enhance debug info related to redis replies

[claudiupb]

Pre-Submission Checklist

• Commit message has the format required by CONTRIBUTING guide
• Commits are split per component (core, individual modules, libs, utils, ...)
• Each component has a single commit (if not, squash them into one commit)
• No commits to README files for modules (changes must be done to docbook files
  in doc/ subfolder, the README file is autogenerated)

Type Of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)

Checklist:

• PR should be backported to stable branches
• Tested changes locally
• Related to issue #XXXX (replace XXXX with an open issue number)

Description

Added a way to print the redis responses when they are arrays, since the previous log message would just print (null) instead. In case a MULTI/EXEC transaction will be used to issue redis commands, the response would be an array, making the original debug message useless. With this new debug, arrays, strings, integers, and other replies such as status or error replies are logged properly.
Also added an error message when a reply is expected but not received.

[miconda]

I think that instead of the above IF condition you can use:

if(!is_printable(log_level))

so redis_get_debug_level() is not needed at all.

[claudiupb]

Yes, this is a lot better. I will change the commit

[claudiupb]

I have modified the commit to use is_printable, instead of defining a new function to get the log level for redis module.