Jenkinsfile: use tags for images

[julianoes]

This should prevent caching issues on Jenkins instances.

[julianoes]

@dagar looks like I don't know groovy:

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:

WorkflowScript: 3: Not a valid section definition: "def docker_ubuntu_1604 = 'dronecore/dronecore-ubuntu-16.04:2018-06-06'". Some extra configuration is required. @ line 3, column 3.

     def docker_ubuntu_1604 = 'dronecore/dronecore-ubuntu-16.04:2018-06-06'

     ^


WorkflowScript: 4: Not a valid section definition: "def docker_ubuntu_1804 = 'dronecore/dronecore-ubuntu-18.04:2018-06-06'". Some extra configuration is required. @ line 4, column 3.

     def docker_ubuntu_1804 = 'dronecore/dronecore-ubuntu-18.04:2018-06-06'

     ^


WorkflowScript: 5: Not a valid section definition: "def docker_fedora_27 = 'dronecore/dronecore-fedora-27:2018-06-06'". Some extra configuration is required. @ line 5, column 3.

     def docker_fedora_27 = 'dronecore/dronecore-fedora-27:2018-06-06'

     ^


WorkflowScript: 6: Not a valid section definition: "def docker_fedora_28 = 'dronecore/dronecore-fedora-28:2018-06-06'". Some extra configuration is required. @ line 6, column 3.

     def docker_fedora_28 = 'dronecore/dronecore-fedora-28:2018-06-06'

I would appreciate your help.

[dagar]

I also don't know groovy. We got away with this only in scripted portions of the PX4 Jenkinsfile. Notice the declarative jobs still use the image and tag directly.

[julianoes]

Thanks @dagar I'll try without the variables, should be simple enough. Let's see if clang-format is there now.