run: capture kernel msg to detect boot errors

Handle boot errors like the old run tool did by checking a kernel
specific string on boot up and start the run script timeout afterwards.

Issue #1395.

tool/run/boot_dir/nova

@@ -24,6 +24,11 @@ proc nova_external { } {
 }
 
 
+proc run_boot_string { } {
+	return "NOVA Microhypervisor"
+}
+
+
 ##
 # Populate directory with binaries on NOVA
 #