lava-submit.jpl: Fix Groovy insecure string interpolation warning

Should not interpolate on Groovy level, instead should do that on shell
level.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: Ib8e680aee665f53ae76ed767e2a78e2e44d918f6
diff --git a/jenkins/lava-submit.jpl b/jenkins/lava-submit.jpl
index f6898a6..9e6cf74 100644
--- a/jenkins/lava-submit.jpl
+++ b/jenkins/lava-submit.jpl
@@ -50,10 +50,10 @@
       --enable-code-coverage "${env.CODE_COVERAGE_EN}"
       """, returnStdout: true).trim()
     print(res)
-    job_ids = sh(script: """./lava_helper/lava_submit_jobs.py \
-      --lava-url ${env.LAVA_URL} --job-dir lava_jobs \
+    job_ids = sh(script: '''./lava_helper/lava_submit_jobs.py \
+      --lava-url ${LAVA_URL} --job-dir lava_jobs \
       --lava-user ${LAVA_USER} --lava-token ${LAVA_TOKEN} | egrep "^JOBS"
-      """, returnStdout: true).trim()
+      ''', returnStdout: true).trim()
     print("${job_ids}")
     currentBuild.setDescription(job_ids)
   }