Use the maximum jitter when calculating the timeout

The timeout should include the maximum possible
jitter since the server will randomly add to it's
timeout a jitter. If the server's timeout is less
than the client's timeout then the client will
return an i/o deadline reached error.

Before:
```
time curl 'http://localhost:8500/v1/catalog/service/service?dc=other-dc&stale=&wait=600s&index=15820644'
rpc error making call: i/o deadline reached
real    10m11.469s
user    0m0.018s
sys     0m0.023s
```

After:
```
time curl 'http://localhost:8500/v1/catalog/service/service?dc=other-dc&stale=&wait=600s&index=15820644'
[...]
real    10m35.835s
user    0m0.021s
sys     0m0.021s
```