Custom consumer tag for federaion.

Proposed Changes

Consumer tag is currently generated from the upstream name. Consumer tag serves to identify a downsream from the upstream queue, while upsream name identifies upstream from the downstream node. It would be more convenient to use different values.

Addresses #66

Types of Changes

What types of changes does your code introduce to this project? Put an x in the boxes that apply

[ ] Bugfix (non-breaking change which fixes issue #NNNN)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[ ] Documentation (correction or otherwise)
[ ] Cosmetics (whitespace, appearance)

Checklist

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[x] I have read the CONTRIBUTING.md document
[x] I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
[x] All tests pass locally with my changes
[x] I have added tests that prove my fix is effective or that my feature works
[ ] I have added necessary documentation (if appropriate)
[ ] Any dependent changes have been merged and published in related repositories

rabbitmq / rabbitmq-federation