Update Linuxkit to v1.7.0

Starting from 1.7.0 Linuxkit uses docker authentication for linuxkit-runner builder

Signed-off-by: Mikhail Malyshev <mike.malyshev@gmail.com>

Author: rucoder

Makefile

@@ -67,7 +67,7 @@ ZARCH ?= $(HOSTARCH)
 export ZARCH
 
 LINUXKIT=$(BUILDTOOLS_DIR)/linuxkit
-LINUXKIT_VERSION=86cc42bf79fde5bba63519313da337144841b647
+LINUXKIT_VERSION=v1.7.0
 LINUXKIT_SOURCE=https://github.com/linuxkit/linuxkit.git
 
 .DEFAULT_GOAL := help