Add command-line flag to enable logs in tests

[gavv]

Currently, logging to console is disabled in tests. This is achieved by to measures:

• log_test.go defines defaultLogLevel LogLevel = LogError; all tests that temporary enable logs, restore log level to this value; this level prevents all log messages except errors

• main_test.go invokes log.SetOutput(ioutil.Discard); all tests that temporary redirect logs, restore log output to ioutil.Discard; this prevents logs to be written to console

However, for debugging, it may be useful to enable console logging.

We can do the following:

• make defaultLogLevel a variable (default is still LogError)
• add new global variable defaultLogOutput (default is ioutil.Discard)
• add command-line flag to tests that enables logs; when the flag is set, defaultLogLevel is set to LogDebug, and defaultLogOutput to console
• at start, tests should set log level and output to defaultLogLevel and defaultLogOutput
• find all tests that call log.SetOutput(ioutil.Discard), and instead use log.SetOutput(defaultLogOutput)

Also, I think it makes sense to rename defaultLogLevel and defaultLogOutput to defaultTestLogLevel and defaultTestLogOutput.

[vraj9845]

@gavv can I please try this?

[gavv]

Sure, thanks!