simulator: panic: invalid argument to Intn

[sonyafenge]

start simulator with the command below and get panic:

/usr/local/go/bin/go run resource-management/test/resourceRegionMgrSimulator/main.go  --region_name=Beijing --rp_num=10 --nodes_per_rp=0000 --master_port=9119 -v=3  > ~/logs/sonya-grs-sim-us-central1-a-0.log 2>&1

Logs from simulator:

I0726 18:31:00.700524    1567 main.go:35]
I0726 18:31:00.700608    1567 main.go:36] Region resource manager simulator config / region name:    (No.Beijing)
I0726 18:31:00.700624    1567 main.go:37] Region resource manager simulator config / rp number per region: (10)
I0726 18:31:00.700633    1567 main.go:38] Region resource manager simulator config / node number per rp:  (0)
I0726 18:31:00.700642    1567 main.go:39]
I0726 18:31:00.700651    1567 main.go:40] Starting resource region manager simulator (Beijing)
I0726 18:31:00.700659    1567 main.go:41]
I0726 18:31:00.700961    1567 simulator.go:60]
Starting resource region manager simulator server on port (9119)
panic: invalid argument to Intn

goroutine 7 [running]:
math/rand.(*Rand).Intn(0xc00003eef0, 0x40e4b4)
        /usr/local/go/src/math/rand/rand.go:168 +0x65
math/rand.Intn(...)
        /usr/local/go/src/math/rand/rand.go:337
global-resource-service/resource-management/test/resourceRegionMgrSimulator/data.makeDataUpdate(0x1bf08eb000)
        /home/sonyali/go/src/global-resource-service/resource-management/test/resourceRegionMgrSimulator/data/regionNodeEvents.go:169 +0x27e
global-resource-service/resource-management/test/resourceRegionMgrSimulator/data.MakeDataUpdate.func1()
        /home/sonyali/go/src/global-resource-service/resource-management/test/resourceRegionMgrSimulator/data/regionNodeEvents.go:53 +0x3e
created by global-resource-service/resource-management/test/resourceRegionMgrSimulator/data.MakeDataUpdate
        /home/sonyali/go/src/global-resource-service/resource-management/test/resourceRegionMgrSimulator/data/regionNodeEvents.go:47 +0x25
exit status 2

[yb01]

the arg is invalid. if this is the cause, we should just invaldate nodes_per_rp to be > 1 or any minimum number it needs.

--nodes_per_rp=0000 

[yb01]

@sonyafenge, please verify

[sonyafenge]

yes, I know. I accidentally put wrong number to env, so found this issue. this is not a blocking issue for testing.
open this issue, just want to suggest we add some basic error check in code to avoid panic.

[q131172019]

PR#126 covers this issue.