fluentd-monasca-output installs legacy fluentd

[yoctozepto]

The culprit is

fluentd-monasca/fluentd-monasca-output.gemspec

Line 19 in 8eec642

spec.add_runtime_dependency 'fluentd', '>= 0.10.43', '<0.14'

This affects Kolla images, making them have a mix of fluentd versions.

[yoctozepto]

Kolla bug report: https://bugs.launchpad.net/kolla/+bug/1955905