Properly fix Travis CI Rabbit MQ issue

[cmonr]

Description

Due to a recent Rabbit MQ migration, Travis CI was failing to run apt-get update successfully. A fix has been placed in master, but involves the use of curl ... | bash which is never a good idea.

While in this case, it shouldn't matter because the script is contained within Travis CI, it still irks me having this pattern associated with the repo at all.

'Fix' to unblock Travis CI introduced here: https://github.com/ARMmbed/mbed-os/pull/8944/files#r238312339

Reference: https://www.idontplaydarts.com/2016/04/detecting-curl-pipe-bash-server-side/

Issue request type

[ ] Question
[ ] Enhancement
[x] Bug

[cmonr]

@ARMmbed/mbed-os-maintainers @ARMmbed/mbed-os-test-team

[cmonr]

Travis support emailed.

[ciarmcom]

Internal Jira reference: https://jira.arm.com/browse/MBOCUSTRIA-248

[cmonr]

Opened #9043 since according to Travis CI support, the issue should be resolved.