Update perf test script

[alexey-yarmosh]

Our npm perf test script worth updating to represent the typical use case.

Current behaviour for every emulated user:

1. Send create measurement request
2. Wait for 202 Accepted
3. Finish

Required behaviour for every emulated user:

1. Send create measurement request
2. Wait for 202 Accepted
3. Send get measurement request
4. Wait for 200 OK and check the status
5. If the status is in-porgress repeat steps 3, 4 with the delay of 1 sec
6. Finish when the status is finished