Create builder/command, cut libcontainer dependency on integration-cli

d1e9d07c introduces a dependency to libcontainer and other daemon
related packages through builder package. The only thing test needs
is set of the Dockerfile commands. Extracting them to a separate
package.

This was causing CI tests to not to compile on non-Linux platforms.

Signed-off-by: Ahmet Alp Balkan <ahmetalpbalkan@gmail.com>
Upstream-commit: ccde3a1f73bb4f64845e736d3173eb6f6935971f
Component: engine

components/engine/builder/command/command.go

@@ -0,0 +1,37 @@
+// This package contains the set of Dockerfile commands.
+package command
+
+const (
+	Env        = "env"
+	Maintainer = "maintainer"
+	Add        = "add"
+	Copy       = "copy"
+	From       = "from"
+	Onbuild    = "onbuild"
+	Workdir    = "workdir"
+	Run        = "run"
+	Cmd        = "cmd"
+	Entrypoint = "entrypoint"
+	Expose     = "expose"
+	Volume     = "volume"
+	User       = "user"
+	Insert     = "insert"
+)
+
+// Commands is list of all Dockerfile commands
+var Commands = []string{
+	Env,
+	Maintainer,
+	Add,
+	Copy,
+	From,
+	Onbuild,
+	Workdir,
+	Run,
+	Cmd,
+	Entrypoint,
+	Expose,
+	Volume,
+	User,
+	Insert,
+}