No separate copy when ephemeral runner is used

When the runner is known to be ephemeral, do not copy the content of the
runner unpacked distribution to the work directory. Instead, run from
there directly and set the RUNNER_BINROOT variable to point to the
installation directory. Ensure that the content of the variable is used
for deciding where to run the runner from and fix directory tree
ownership prior to starting the runner.

Rename the label to krun, instead of krunvm. This is to highlight the
underlying technology used, rather than how the runners are created.
This is a breaking change, but it is not expected to be used in
production yet.

runner/entrypoint.sh

@@ -100,6 +100,9 @@ RUNNER_CONTAINERS_CONF="${RUNNER_CONTAINERS_CONFDIR%/}/containers.conf"
 # Location of the directory where the runner scripts and binaries will log
 RUNNER_LOGDIR=${RUNNER_LOGDIR:-"/var/log/runner"}
 
+# Default set of labels to attach to the runner when none set
+RUNNER_DEFAULT_LABELS=${RUNNER_DEFAULT_LABELS:-"krun"}
+
 # shellcheck disable=SC2034 # Used in sourced scripts
 KRUNVM_RUNNER_DESCR="Configure and run the installed GitHub runner"
 
@@ -161,13 +164,18 @@ KRUNVM_RUNNER_BIN="${KRUNVM_RUNNER_BIN%.sh}-$RUNNER_ID"
 # minimal verification of the installation through checking that there is a
 # config.sh script executable within the copy.
 runner_install() {
-  if ! [ -d "${RUNNER_WORKDIR%/}" ]; then
-    mkdir -p "${RUNNER_WORKDIR%/}"
-    verbose "Created runner directory ${RUNNER_WORKDIR%/}"
+  if is_true "$RUNNER_EPHEMERAL"; then
+    debug "Ephemeral runner: no copy made, running from $RUNNER_INSTDIR"
+    RUNNER_BINROOT="$RUNNER_INSTDIR"
+  else
+    if ! [ -d "${RUNNER_WORKDIR%/}" ]; then
+      mkdir -p "${RUNNER_WORKDIR%/}"
+      verbose "Created runner directory ${RUNNER_WORKDIR%/}"
+    fi
+    RUNNER_BINROOT="${RUNNER_WORKDIR%/}/runner"
+    verbose "Copying runner installation to $RUNNER_BINROOT"
+    cp -rf "$RUNNER_INSTDIR" "$RUNNER_BINROOT" 2>/dev/null
   fi
-  RUNNER_BINROOT="${RUNNER_WORKDIR%/}/runner"
-  verbose "Copying runner installation to $RUNNER_BINROOT"
-  cp -rf "$RUNNER_INSTDIR" "$RUNNER_BINROOT" 2>/dev/null
   check_command "${RUNNER_BINROOT}/config.sh"
 }
 
@@ -403,9 +411,9 @@ RUNNER_NAME=${RUNNER_NAME:-"${RUNNER_PREFIX}-$RUNNER_ID"}
 
 RUNNER_WORKDIR=${RUNNER_WORKDIR:-"/_work/${RUNNER_NAME}"}
 if [ -n "${distro:-}" ]; then
-  RUNNER_LABELS=${RUNNER_LABELS:-"krunvm,${RUNNER_DISTRO}"}
+  RUNNER_LABELS=${RUNNER_LABELS:-"${RUNNER_DEFAULT_LABELS%,},${RUNNER_DISTRO}"}
 else
-  RUNNER_LABELS=${RUNNER_LABELS:-"krunvm"}
+  RUNNER_LABELS=${RUNNER_LABELS:-"${RUNNER_DEFAULT_LABELS%,}"}
 fi
 
 # Find the (versioned) directory containing the full installation of the runner
@@ -449,7 +457,7 @@ runner_configure
 
 if [ "$#" = 0 ]; then
   warn "No command to run, will take defaults"
-  set -- "${RUNNER_WORKDIR%/}/runner/bin/Runner.Listener" run --startuptype service
+  set -- "${RUNNER_BINROOT%/}/bin/Runner.Listener" run --startuptype service
 fi
 
 # Capture termination signals. Pass a boolean to runner_unregister: don't break
@@ -480,7 +488,7 @@ case "$RUNNER_USER" in
     if id "$RUNNER_USER" >/dev/null 2>&1; then
       if [ "$(id -u)" = "0" ]; then
         verbose "Starting runner as $RUNNER_USER"
-        chown -R "$RUNNER_USER" "$RUNNER_WORKDIR"
+        chown -R "$RUNNER_USER" "$RUNNER_WORKDIR" "$RUNNER_BINROOT"
         runas "$@" > "$RUNNER_LOGDIR/runner.log" 2>&1 &
         RUNNER_PID=$!
       elif [ "$(id -un)" = "$RUNNER_USER" ]; then