Add staticcheck linter

Fix issues with sync.Pool being passed an array and not a pointer.
See https://github.com/dominikh/go-tools/blob/master/cmd/staticcheck/docs/checks/SA6002

Add missing tests for content.Copy

Fix T.Fatal being called in a goroutine

Signed-off-by: Daniel Nephin <dnephin@gmail.com>

fs/copy.go

@@ -9,13 +9,12 @@ import (
 	"github.com/pkg/errors"
 )
 
-var (
-	bufferPool = &sync.Pool{
-		New: func() interface{} {
-			return make([]byte, 32*1024)
-		},
-	}
-)
+var bufferPool = &sync.Pool{
+	New: func() interface{} {
+		buffer := make([]byte, 32*1024)
+		return &buffer
+	},
+}
 
 // CopyDir copies the directory from src to dst.
 // Most efficient copy of files is attempted.