refac: rename degrad -> degrad_space, #18

src/users/broker.cpp

src/users/response_behaviors.cpp

src/users/user_windows.cpp

...dm_user_multi_behavior-2machines_user_stats_behaviors.csv

...avior_small_workload_1-2machines_user_stats_behaviors.csv

...avior_small_workload_4-2machines_user_stats_behaviors.csv

...avior_small_workload_5-2machines_user_stats_behaviors.csv

..._multi_behavior_yellow-2machines_user_stats_behaviors.csv