Make repository_uploader to support S3_FILES_TO_UPLOAD

[j-rivero]

Change in repository_uploader to be able to pass files directly to the S3 uploaders by naming them exactly. This should help with the right upload of new tarballs generated in Jenkins.

The repository_uploader_packages job does not have a DSL definition yet but I have tested the execution of the code in an expected failed build to be sure that the uploader does not fail when there is no package specified and just the normal use of uploading .deb packages and source packages.

...
+ case ${UPLOAD_TO_REPO} in
+ ENABLE_S3_UPLOAD=false
++ find /home/jenkins/workspace/repository_uploader_packages/pkgs -type f -name '*.zip' -printf '%f\n'
+ S3_FILES_TO_UPLOAD=' '
++ find /home/jenkins/workspace/repository_uploader_packages/pkgs -name '*.bottle*.json'
+ [[ nightly == \o\n\l\y\_\s\3\_\u\p\l\o\a\d ]]
+ LINUX_DISTRO=ubuntu
+ repo_path=/var/packages/gazebo/ubuntu-nightly
+ [[ ! -d /var/packages/gazebo/ubuntu-nightly ]]
...

[j-rivero]

Merging to give it some testing before other changes landed.