jenkins/criu-lazy-migration: clean old files

Otherwise files from a previous build can affect the current one.

Reported-by: Mr Jenkins
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

test/jenkins/criu-lazy-migration.pipeline

@@ -13,6 +13,7 @@ pipeline {
 	stages {
 		stage('Build') {
 			steps {
+				sh 'git clean -dxf'
 				sh 'make'
 				sh 'make -C test/zdtm'
 			}