[yugabyted] Restarting a node fails when `data_dir` is missing in user specified configuration.

[ShikharSahay]

Jira Link: DB-11983

Description

When restarting yugabyted with a user configuration file that does not contain the data_dir parameter, an AttributeError is raised because the code attempts to call split on a NoneType object.

Content of user config file -

13:03 ~/test $ cat user.test 
{
    "tserver_flags": "enable_automatic_tablet_splitting=false,ysql_pg_conf_csv={yb_bnl_batch_size=2048},ysql_hba_conf_csv={host all all 0.0.0.0/0 md5,host all all ::0/0 md5,host all all 0.0.0.0/0 scram-sha-256,host all all ::0/0 scram-sha-256}",
    "master_flags": "enable_automatic_tablet_splitting=false"
}
13:03 ~/test $ 

Steps to reproduce the issue:

1. Start the yugabyted node using:
   ./yugabyted start --config /net/dev-server-ssahay/share/test/user.test
2. Stop the yugabyted node
3. Restart the yugabyted node using:
   ./yugabyted start --config /net/dev-server-ssahay/share/test/user.test

We get the following error:

12:45 ~/code/yugabyte-db/bin [master] $ ./yugabyted start --config /net/dev-server-ssahay/share/test/user.test
Traceback (most recent call last):
  File "./yugabyted", line 8765, in <module>
    ControlScript().run()
  File "./yugabyted", line 6730, in run
    self.validate_and_set_parent_configs(args)
  File "./yugabyted", line 5199, in validate_and_set_parent_configs
    self.configs = self.handle_config_files(args, conf_dir, self.conf_file, base_dir)
  File "./yugabyted", line 5150, in handle_config_files
    path for path in user_configs.get("data_dir").split(',')
AttributeError: 'NoneType' object has no attribute 'split'
12:45 ~/code/yugabyte-db/bin [master] $ 

Warning: Please confirm that this issue does not contain any sensitive information

• I confirm this issue does not contain any sensitive information.

[ShikharSahay]

Code changes landed.