alpine: Update to containerd v1.0.0-alpha2

Signed-off-by: Ian Campbell <ijc@docker.com>

tools/alpine/Dockerfile

@@ -52,6 +52,5 @@ COPY --from=mirror /Dockerfile /Dockerfile
 RUN apk update && apk upgrade -a
 
 # Update `FROM` in `test/pkg/containerd/Dockerfile` when changing this.
-# v1.0.0-alpha1 plus https://github.com/containerd/containerd/pull/1141
-ENV CONTAINERD_REPO=https://github.com/ijc/containerd.git
-ENV CONTAINERD_COMMIT=d42cb88ba2b08d2ca6c8c017d629b394bf1dd08c
+ENV CONTAINERD_REPO=https://github.com/containerd/containerd.git
+ENV CONTAINERD_COMMIT=v1.0.0-alpha2

tools/alpine/versions.x86_64

@@ -1,4 +1,4 @@
-# linuxkit/alpine:77c8dfc5860012c869a19d7a2c68e701469692c8
+# linuxkit/alpine:cb6a0b2b068d892996ebadae999d9baf6e08be5b
 # automatically generated list of installed packages
 abuild-3.0.0_rc2-r8
 alpine-baselayout-3.0.4-r0
@@ -91,14 +91,14 @@ libattr-2.4.47-r6
 libblkid-2.28.2-r2
 libburn-1.4.6-r0
 libbz2-1.0.6-r5
-libc-dev-0.7.1-r0
-libc-utils-0.7.1-r0
 libcap-2.25-r1
 libcap-ng-0.7.8-r0
 libcap-ng-dev-0.7.8-r0
+libc-dev-0.7.1-r0
 libcom_err-1.43.4-r0
 libcrypto1.0-1.0.2k-r0
 libcurl-7.54.0-r0
+libc-utils-0.7.1-r0
 libdrm-2.4.80-r0
 libedit-20170329.3.1-r2
 libelf-0.8.13-r2
@@ -131,10 +131,10 @@ libpcap-1.8.1-r0
 libpciaccess-0.13.4-r1
 libpng-1.6.29-r1
 libressl-2.5.4-r0
-libressl-dev-2.5.4-r0
 libressl2.5-libcrypto-2.5.4-r0
 libressl2.5-libssl-2.5.4-r0
 libressl2.5-libtls-2.5.4-r0
+libressl-dev-2.5.4-r0
 libsasl-2.1.26-r10
 libseccomp-2.3.2-r0
 libseccomp-dev-2.3.2-r0
@@ -175,12 +175,12 @@ ncurses-terminfo-base-6.0-r7
 nettle-3.3-r0
 npth-1.2-r0
 oniguruma-6.2.0-r0
-open-vm-tools-10.1.0-r7
 openntpd-6.0_p1-r3
 openrc-0.24.1-r2
 openssh-keygen-7.5_p1-r1
 openssh-server-7.5_p1-r1
 openssl-dev-1.0.2k-r0
+open-vm-tools-10.1.0-r7
 opus-1.1.4-r0
 ovmf-0.0.20161115-r1
 p11-kit-0.23.2-r1