test: update Dockerfile to install socat and ssdp[cli]

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

test/docker/Dockerfile

@@ -15,6 +15,7 @@ RUN apk add --no-cache \
     qemu-img \
     qemu-system-x86_64 \
     ruby-mustache \
+    socat \
     squashfs-tools \
     tcpdump
 

test/docker/README.md

@@ -8,6 +8,10 @@ The following is a checklist/reminder to maintainers for how to update
 the image, e.g., with missing Alpine packages.
 
  1. Update the Dockerfile
+
+        cd test/docker/
+        edit Dockerfile
+
  2. Build the new image version, for latest version, see released images
     here: <https://github.com/kernelkit/infix/pkgs/container/infix-test>
 	in this example we use version 0.4:

test/docker/pip-requirements.txt

@@ -5,3 +5,4 @@ networkx==3.1
 pydot==1.4.2
 pyyaml==5.4.1
 passlib==1.7.4
+ssdp[cli]==1.3.0