Creates a `fixedBuffer` type that is used to encapsulate functionality
for reading/writing from the underlying byte slices.
Uses lazily-loaded set of sync.Pools for storing buffers that are no
longer needed so they can be re-used.
```
benchmark old ns/op new ns/op delta
BenchmarkBytesPipeWrite-8 138469 48985 -64.62%
BenchmarkBytesPipeRead-8 130922 56601 -56.77%
benchmark old allocs new allocs delta
BenchmarkBytesPipeWrite-8 18 8 -55.56%
BenchmarkBytesPipeRead-8 0 0 +0.00%
benchmark old bytes new bytes delta
BenchmarkBytesPipeWrite-8 66903 1649 -97.54%
BenchmarkBytesPipeRead-8 0 1 +Inf%
```
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
This is a small configuration struct used in two scenarios:
1. To attach I/O pipes to a running containers.
2. To attach to execution processes inside running containers.
Although they are similar, keeping the struct in the same package
than exec and container can generate cycled dependencies if we
move any of them outside the daemon, like we want to do
with the container.
Signed-off-by: David Calavera <david.calavera@gmail.com>
