tools: Add a few more packages to the Alpine base image

- iproute2 provides a more complete suite of 'ip' utilities than
  the busybox implementation. Useful, for debugging.
- iperf3 for network testing
- tcpdump for network debugging
- expect is used in some tests. Adding it to the base image should
  make it easier to create a LinuxKit image to self-host CI.

The new version of the base package is:
linuxkit/alpine:3d57ded3edd54e616210cf0c17e3bc15eed9d03a

Signed-off-by: Rolf Neugebauer <rolf.neugebauer@docker.com>

tools/alpine/packages

@@ -25,6 +25,7 @@ dosfstools
 e2fsprogs
 e2fsprogs-extra
 elfutils-dev
+expect
 flex
 gcc
 git
@@ -34,6 +35,8 @@ go
 gummiboot
 hvtools
 installkernel
+iperf3
+iproute2
 iptables
 jq
 kmod
@@ -71,6 +74,7 @@ strace
 swig
 syslinux
 tar
+tcpdump
 tini
 tzdata
 util-linux

tools/alpine/versions

@@ -40,6 +40,7 @@ e2fsprogs-libs-1.43.4-r0
 elfutils-dev-0.168-r1
 elfutils-libelf-0.168-r1
 expat-2.2.0-r1
+expect-5.45-r3
 fakeroot-1.21-r1
 file-5.30-r0
 findmnt-2.28.2-r2
@@ -63,6 +64,8 @@ gummiboot-48.1-r0
 hvtools-4.4.15-r0
 icu-libs-58.2-r2
 installkernel-3.5-r0
+iperf3-3.1.7-r0
+iproute2-4.10.0-r1
 iptables-1.6.1-r0
 isl-0.17.1-r0
 jq-1.5-r3
@@ -117,6 +120,7 @@ libmspack-0.5_alpha-r0
 libnfs-1.11.0-r0
 libnftnl-libs-1.0.7-r0
 libogg-1.3.2-r1
+libpcap-1.8.1-r0
 libpciaccess-0.13.4-r1
 libpng-1.6.29-r1
 libressl-2.5.4-r0
@@ -200,6 +204,8 @@ sudo-1.8.19_p2-r0
 swig-3.0.10-r0
 syslinux-6.04_pre1-r1
 tar-1.29-r1
+tcl-8.6.6-r0
+tcpdump-4.9.0-r1
 tini-0.14.0-r0
 tzdata-2017a-r0
 usbredir-0.7-r2