The version of erlang we're using, while functional, is not recommended.
This change updates our version of erlang for rabbitmq to be the
recommended version by changing the pinned version of erlang.
The apt package pinning meta dependency has been removed and put into
the apt task file as an include role. To ensure a more uniform process
for setting the version of erlang used with rabbitmq the new variable
`rabbitmq_erlang_version_spec` has been added. This option has a default
of "null" and is set by distro specific variables when applicable.
Erlang version support matrix: https://www.rabbitmq.com/which-erlang.html
Change-Id: Iced12d4533eec068bd11d8bd235d81308ef40427
Signed-off-by: Kevin Carter <kevin.carter@rackspace.com>
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