Canary release weight ratio doesn't work as expected

[WxFang]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce

Route same prefix to different services A and B.

1. If weight_A+weight_B != 100, then only when weight_A/weight_B == 1 or 3 or 4 or 9 this route change will be applied. Or it will be ignored. Amabassador is trying to make normalized weight to be certain numbers.
2. Another weird issue is that when weight_A = 0 and weight_B = 100, route table will appear 100:100.

Set weights as below and check the route table:
weight_A = 10, weight_B=10
weight_A = 10, weight_B=30
weight_A = 10, weight_B=40
weight_A = 10, weight_B=90
weight_A = 60, weight_B=60
weight_A = 60, weight_B=180
weight_A = 60, weight_B=240
weight_A = 60, weight_B=540

Expected behavior
Whatever the sum is, two weights will be normalized and this change will be applied.

Versions (please complete the following information):

• Ambassador: [0.50.3]
• Kubernetes environment [bare metal]
• Version [v1.13.1]