CLI tests for logging flags (#3609)

## Issue Addressed
Adding CLI tests for logging flags: log-color and disable-log-timestamp
Which issue # does this PR address?
#3588 
## Proposed Changes
Add CLI tests for logging flags as described in #3588 
Please list or describe the changes introduced by this PR.
Added logger_config to client::Config as suggested. Implemented Default for LoggerConfig based on what was being done elsewhere in the repo. Created 2 tests for each flag addressed.
## Additional Info

Please provide any additional information. For example, future considerations
or information useful for reviewers.

lighthouse/src/main.rs

@@ -438,9 +438,9 @@ fn run<E: EthSpec>(
 
     let logger_config = LoggerConfig {
         path: log_path,
-        debug_level,
-        logfile_debug_level,
-        log_format,
+        debug_level: String::from(debug_level),
+        logfile_debug_level: String::from(logfile_debug_level),
+        log_format: log_format.map(String::from),
         log_color,
         disable_log_timestamp,
         max_log_size: logfile_max_size * 1_024 * 1_024,
@@ -448,7 +448,7 @@ fn run<E: EthSpec>(
         compression: logfile_compress,
     };
 
-    let builder = environment_builder.initialize_logger(logger_config)?;
+    let builder = environment_builder.initialize_logger(logger_config.clone())?;
 
     let mut environment = builder
         .multi_threaded_tokio_runtime()?
@@ -528,7 +528,8 @@ fn run<E: EthSpec>(
             let context = environment.core_context();
             let log = context.log().clone();
             let executor = context.executor.clone();
-            let config = beacon_node::get_config::<E>(matches, &context)?;
+            let mut config = beacon_node::get_config::<E>(matches, &context)?;
+            config.logger_config = logger_config;
             let shutdown_flag = matches.is_present("immediate-shutdown");
             // Dump configs if `dump-config` or `dump-chain-config` flags are set
             clap_utils::check_dump_configs::<_, E>(matches, &config, &context.eth2_config.spec)?;