Make retries more aggressive in Nerd
Make retries more aggressive in Nerd

The previous retry logic inside the `State` and `loadContainerAndTask`
methods was sleeping for 2^n seconds after every attempt (where n = number
of attempts), with a timeout of 5 seconds. This meant making a maximum
of 3 attempts (after 0, 1 and 3 seconds). I'm moving this to a fixed
500ms sleep, so that we can try a maximum of 10 times.

[#170130226]

cloudfoundry-incubator/guardian,cloudfoundry-incubator/guardian,cloudfoundry-incubator/guardian