[FEA] Fix empty softwareProperties field in worker_info.yaml file for profiling tool

[cindyyuanjiang]

Fixes #608

Currently, when the worker_info.yaml file has empty softwareProperties field as below, the profiling tool throws a null pointer exception.

system:
  numCores: 32
  memory: 212992MiB
  numWorkers: 5
gpu:
  memory: 15109MiB
  count: 4
  name: T4
softwareProperties:

We work around this by assigning an empty LinkedHashMap (default) to softwareProperties if it is null after loading the worker_info.yaml file into a ClusterProperties instance.

[parthosa]

Thanks @cindyyuanjiang.