Comment 2 for bug 1395814

As explained on IRC:

.:fungi:. basically if you have package A already installed at version 1.2.3 and then feed pip a list of packages to install (directly or transitively) if the first dependency it sees listed on package A doesn't require newer than 1.2.3 then a later listed dependency on A>=2.3.4 will basically be ignored and won't trigger an upgrade

Issue here is ceilometer and glance both list oslo.vmware but their 'eventlet>=0.13.0' trumps oslo.vmware's 'eventlet>=0.15.1' when installed via pip. In the past, oslo.vmware was installed on its own by devstack via git checkout, but https://review.openstack.org/#/c/136335/ changed that and its now up to pip to sort this out transitively, and it turns out that doesn't work well.

I've put up https://review.openstack.org/#/c/136879/ to cap oslo.vmware on stable/icehouse to 0.5.0, which was the last version that its eventlet requirement matched the rest of stable/icehouse.