The "prepare-packaes" ant target is not skipped when skipping tests, resulting in an unneeded copy of jars useful for tests, as seen on similar explorer tests:
11:48:47 [INFO] --- ant-assembly-maven-plugin:2.1.4:build (start-tomcat) @ nuxeo-explorer-ftests-nomode ---
11:48:47 [INFO] Active Maven profiles:
11:48:47 nexus (source: external)
11:48:47 release (source: org.nuxeo:nuxeo-ecm:11.3.15)
11:48:47 os-notwindows (source: org.nuxeo:nuxeo-ecm:11.3.15)
11:48:47 [INFO] Managed version set on org.nuxeo:nuxeo-ftest:zip:1.8.8
11:48:47 [INFO] [unzip] Expanding: /root/.mvnrepository/org/nuxeo/nuxeo-ftest/1.8.8/nuxeo-ftest-1.8.8.zip into /home/jenkins/workspace/nuxeo/release-nuxeo-explorer/ftests/explorer-ftests-nomode/target
11:48:47 [INFO] [copy] Copying 1 file to /home/jenkins/workspace/nuxeo/release-nuxeo-explorer/ftests/explorer-ftests-nomode/target/packages
11:48:47 [INFO] Tests are skipped (skipTests=true).
11:48:47 [INFO] --- maven-failsafe-plugin:2.22.2:integration-test (default) @ nuxeo-explorer-ftests-nomode ---
11:48:47 [INFO] Tests are skipped.
Making the _init target the first one to be executed would fix it.