ci: add s390x vmtest

Run it on the self-hosted builder with tag "z15".

Also add the infrastructure code for the self-hosted builder.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>

travis-ci/vmtest/s390x-self-hosted-builder/fs/usr/bin/actions-runner

@@ -0,0 +1,40 @@
+#!/bin/bash
+
+#
+# Ephemeral runner startup script.
+#
+# Expects the following environment variables:
+#
+# - repo=<owner>/<name>
+# - access_token=<ghp_***>
+#
+
+set -e -u
+
+# Check the cached registration token.
+token_file=registration-token.json
+set +e
+expires_at=$(jq --raw-output .expires_at "$token_file" 2>/dev/null)
+status=$?
+set -e
+if [[ $status -ne 0 || $(date +%s) -ge $(date -d "$expires_at" +%s) ]]; then
+    # Refresh the cached registration token.
+    curl \
+        -X POST \
+        -H "Accept: application/vnd.github.v3+json" \
+        -H "Authorization: token $access_token" \
+        "https://api.github.com/repos/$repo/actions/runners/registration-token" \
+        -o "$token_file"
+fi
+
+# (Re-)register the runner.
+registration_token=$(jq --raw-output .token "$token_file")
+./config.sh remove --token "$registration_token" || true
+./config.sh \
+    --url "https://github.com/$repo" \
+    --token "$registration_token" \
+    --labels z15 \
+    --ephemeral
+
+# Run one job.
+./run.sh

travis-ci/vmtest/s390x-self-hosted-builder/fs/usr/bin/entrypoint

@@ -0,0 +1,35 @@
+#!/bin/bash
+
+#
+# Container entrypoint that waits for all spawned processes.
+#
+
+set -e -u
+
+# /dev/kvm has host permissions, fix it.
+if [ -e /dev/kvm ]; then
+    sudo chown root:kvm /dev/kvm
+fi
+
+# Create a FIFO and start reading from its read end.
+tempdir=$(mktemp -d "/tmp/done.XXXXXXXXXX")
+trap 'rm -r "$tempdir"' EXIT
+done="$tempdir/pipe"
+mkfifo "$done"
+cat "$done" & waiter=$!
+
+# Start the workload. Its descendants will inherit the FIFO's write end.
+status=0
+if [ "$#" -eq 0 ]; then
+    bash 9>"$done" || status=$?
+else
+    "$@" 9>"$done" || status=$?
+fi
+
+# When the workload and all of its descendants exit, the FIFO's write end will
+# be closed and `cat "$done"` will exit. Wait until it happens. This is needed
+# in order to handle SelfUpdater, which the workload may start in background
+# before exiting.
+wait "$waiter"
+
+exit "$status"