According to https://github.com/golang/go/issues/5373, go recognizes
(and optimizes for) the following syntax:
```go
for i := range b {
b[i] = 0
}
```
so let's use it. Limited testing shows ~7.5x speed increase,
compared to the previously used syntax.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
This helper acts like /dev/zero (outputs \x00 indefinitely) in an
OS-independent fashion. This ensures we don't need to special-case
around Windows in tests that want to open /dev/zero.
Signed-off-by: Aleksa Sarai <asarai@suse.de>
split all non-cli portions into a new internal/test/environment package
Set a test environment on packages instead of creating new ones.
Signed-off-by: Daniel Nephin <dnephin@docker.com>
