All locusts dead: runners.py has round error when percent is value that rounds to zero

[markmen3599]

Description of issue / feature request

I am running two client classes inside of a locust file. When I run with --no-web -c 1 -r 1 for testing purposes, the runner was not starting and showing this in the logs:

[2018-12-17 14:40:38,640] ubuntu/INFO/locust.runners: Hatching and swarming 0 clients at the rate 1 clients/s...
[2018-12-17 14:40:38,640] ubuntu/INFO/locust.runners: All locusts hatched: ScenarioPOSTGET: 0, ScenarioPOSTPUTGET: 0
[2018-12-17 17:11:35,855] ubuntu/INFO/locust.runners: All locusts dead

The problem is in runners.py.weight_locusts.py; lines 82 & 83 (see below)

    def weight_locusts(self, amount, stop_timeout = None):
        """
        Distributes the amount of locusts for each WebLocust-class according to it's weight
        returns a list "bucket" with the weighted locusts
        """
        bucket = []
        weight_sum = sum((locust.weight for locust in self.locust_classes if locust.task_set))
        for locust in self.locust_classes:
            if not locust.task_set:
                warnings.warn("Notice: Found Locust class (%s) got no task_set. Skipping..." % locust.__name__)
                continue

            if self.host is not None:
                locust.host = self.host
            if stop_timeout is not None:
                locust.stop_timeout = stop_timeout

            # create locusts depending on weight
            percent = locust.weight / float(weight_sum) # this is 0.5
            num_locusts = int(round(amount * percent)) # round of 0.5 is -> '0'  :(
            bucket.extend([locust for x in xrange(0, num_locusts)])
        return bucket

Recommend using math.ceil if percent < 1

Expected behavior

The runner should execute my 2 scenarios in this situation.

Actual behavior

It does not and shows the locusts are dead.

Environment settings (for bug reports)

• OS: ubuntu 18.04
• Python version: 3.6.6
• Locust version: 0.9.0

Steps to reproduce (for bug reports)

1. Create a test with 2 client classes:
   e.g.

class ScenarioPOSTGET(HttpLocust):
    print("inside ScenarioPOSTGET")
    task_set = PostAndGetTask
    host = "http://10.203.0.70:30112"

class ScenarioPOSTPUTGET(HttpLocust):
    print("inside PostPutAndGetTasks")
    task_set = PostPutAndGetTasks
    host = "http://10.203.0.70:30112"

Run this way:
locust -f locust_test.py --no-web -c 1 -r 1 --run-time 8s

[heyman]

Fixed by #1113