Post-review fixes for WL#2713 "Change IM behaviour so, that it only reads and alters one config file only."


server-tools/instance-manager/commands.cc:
  get rid of single_defaults_file_option and use Options::config_file instead
server-tools/instance-manager/commands.h:
  get rid of single_defaults_file_option and use Options::config_file instead
server-tools/instance-manager/instance_map.cc:
  get rid of single_defaults_file_option and use Options::config_file instead
server-tools/instance-manager/instance_map.h:
  get rid of single_defaults_file_option and use Options::config_file instead
server-tools/instance-manager/manager.cc:
  get rid of single_defaults_file_option and use Options::config_file instead
server-tools/instance-manager/options.cc:
  Disable --defaults-extra-file and --no-defaults options for the IM as they have no sence. 
  Don't use print_defaults as it prints out wrong "first option" information for IM. Use only
  Options::config_file to process options
server-tools/instance-manager/options.h:
  get rid of single_defaults_file_option and use Options::config_file instead