Added basic command line argument error messages to Client.java
Added basic command line argument error messages to Client.java

madhurihn/YCSB_ToyDB,madhurihn/YCSB_ToyDB,ChristianNavolskyi/YCSB,zyguan/ycsb,ChristianNavolskyi/YCSB,jaemyoun/YCSB,brianfrankcooper/YCSB,brianfrankcooper/YCSB,jaemyoun/YCSB,madhurihn/YCSB_ToyDB,leschekhomann/YCSB,madhurihn/YCSB_ToyDB,zyguan/ycsb,jaemyoun/YCSB,leschekhomann/YCSB,brianfrankcooper/YCSB,ChristianNavolskyi/YCSB,cricket007/YCSB,manolama/YCSB,leschekhomann/YCSB,cricket007/YCSB,zyguan/ycsb,leschekhomann/YCSB,zyguan/ycsb,ChristianNavolskyi/YCSB,brianfrankcooper/YCSB,manolama/YCSB,manolama/YCSB,manolama/YCSB,cricket007/YCSB,jaemyoun/YCSB,cricket007/YCSB