MINOR: Pass `--continue` to gradle in jenkins.sh

This ensures that the whole test suite is executed even
if there are failures. It currently stops at a module
boundary if there are any failures. There is a discussion
to change the gradle default to stop after the first test failure:

https://github.com/gradle/gradle/issues/6513

`--continue` is recommended for CI in that discussion.

Author: Ismael Juma <ismael@juma.me.uk>

Reviewers: Dong Lin <lindong28@gmail.com>

Closes #5599 from ijuma/jenkins-script-continue

jenkins.sh

@@ -17,4 +17,4 @@
 # This script is used for verifying changes in Jenkins. In order to provide faster feedback, the tasks are ordered so
 # that faster tasks are executed in every module before slower tasks (if possible). For example, the unit tests for all
 # the modules are executed before the integration tests.
-./gradlew clean compileJava compileScala compileTestJava compileTestScala spotlessScalaCheck checkstyleMain checkstyleTest findbugsMain unitTest rat integrationTest --no-daemon -PxmlFindBugsReport=true -PtestLoggingEvents=started,passed,skipped,failed "$@"
+./gradlew clean compileJava compileScala compileTestJava compileTestScala spotlessScalaCheck checkstyleMain checkstyleTest findbugsMain unitTest rat integrationTest --no-daemon --continue -PxmlFindBugsReport=true -PtestLoggingEvents=started,passed,skipped,failed "$@"