test: Allow a tmux pane to watch commands executed in contexts

We're moving to a new way of the tests dispatching commands to running in
contexts (host, guest, namespace, etc.).  As we make this transition,
though, we still want the user to be able to watch the commands running
in a context, as they previously could from the commands issued in the
pane.

Add a helper to set up a pane to watch a context's log to allow this.  In
some cases we currently issue commands from several different logical
contexts in the same pane, so allow a pane to watch several contexts at
once.  Also use tail's --retry option to allow starting the watch before
we've initialized the context which will be useful in some cases.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

test/lib/term

@@ -241,6 +241,24 @@ pane_status() {
 	return ${__status}
 }
 
+# pane_watch_context() - Set up pane to watch commands executing in context(s)
+# $1:	Pane number
+# $2:	Description (for pane label)
+# $@:	Context name or names
+pane_watch_contexts() {
+	__pane_number="${1}"
+	__desc="${2}"
+	shift 2
+	__name="${2}"
+
+	tmux select-pane -t ${__pane_number} -T "${__desc}"
+	__cmd="tail -f --retry"
+	for c; do
+		__cmd="${__cmd} ${LOGDIR}/context_${c}.log"
+	done
+	cmd_write ${__pane_number} "${__cmd}"
+}
+
 # status_file_end() - Display and log messages when tests from one file are done
 status_file_end() {
 	[ -z "${STATUS_FILE}" ] && return