featureflag: update generations flag to support branches and generations

Question

Checklist

• [x] Checked if it requires a pylibjuju change?
• [] Added integration tests for the PR?
• [] Added or updated doc.go related to packages changed?
• [x] Do comments answer the question of why design decisions were made?

Description of change`

• we changed the featureflag generations/branches name from 2.7 to develop. This patch enables to use both for UX.

• acceptancetest test-branches fix ensure that we wait for add-branch before asking for it.

QA steps

any branches/generations cli command (add-branch...) set the either of the dev_flags and test the commands

sh
export JUJU_DEV_FEATURE_FLAGS=generations
juju add-branch blub

sh
export JUJU_DEV_FEATURE_FLAGS=branches
juju add-branch bla

don't export the respective featureflag

sh
juju add-branch bla
ERROR juju: "add-branch" is not a juju command. See "juju --help".

Did you mean:
    add-space

该提问来源于开源项目：juju/juju

Answer 1

unrelated to this aptch..

    c.Assert(funcErr, jc.ErrorIsNil)
... value *errors.Err = &errors.unformatter{message:"got 0 timers added after 

!!build!!