Use time.Duration as type for timeouts

[pdalpra]

This PR replaces instances of where timeout was an int representing the number of seconds by time.Duration, as suggested by #230 .
Not entirely sure about the float64 -> int conversion, also thought about using strconv.FormatFloat(v, 'f', 0, 64) for formatting it as an integer. WDYT ?

[vdemeester]

@pdalpra cool 👍 Using strconv.FormatFloat makes more sence to me (reading it at least).

[pdalpra]

should I introduce this as a utility function or inline the code for the time being ?

[vdemeester]

@pdalpra maybe a utility function it types/time 😝

[pdalpra]

sorry for keeping it stale, will update the PR today

[pdalpra]

@vdemeester PR (finally !) updated

[vdemeester]

LGTM 👼
/cc @aaronlehmann @calavera

[pdalpra]

I can take of the matching PR on docker/docker if you like

[calavera]

LGTM

[MHBauer]

I'm a bit late to the review.

First, great thought and contribution @pdalpra. It is much appreciated and I think it is good practice to use time.Durations for our timeout durations.

I do not like that we convert an int to a float then parse the float to convert to a string.

1. Too much conversion when it should be just number to number. (This is more of an aesthetics thing)
2. This adopts float semantics for an integer. (I think this is mainly to be used with full seconds, so it does not matter so much)

My suggestion would to be add a comment on the rounding, just so no-one expects to get sub second precision, or to adopt what is in the godocs for time.Duration, i.e. the calculation becomes int64(duration/time.Second) instead of the float/string parsing. That also does a rounding (always round down) with no sub second precision.

Thanks again @pdalpra for the contribution here and in moby/moby#23344!