Initializing new series requires fiddling with publisher setup

Currently, we need to disable the publisher during distroseries initialization (see https://wiki.ubuntu.com/NewReleaseCycleProcess step 5). Since initializing a distro series is a normal (if uncommon) part of operation, it should not require any fiddling with any publisher internals.

<jml> wgrant: did you say there was a bug for need to disable the publisher during distroseries initialisation?
<wgrant> jml: I don't think there is. In the context of the whole process (with the extra careful runs later on) it will probably work fine, but it needs testing.
<cjwatson> we'd have to disable the cron job for the manual careful runs anyway
<cjwatson> so the fact that the careful runs are needed is a bug, if you want to look at it that way
<cjwatson> (i.e. should be possible to initialise new series without fiddling with publisher setup)
<wgrant> We want to make dirty pockets forcable for other reasons anyway, which would eliminate the need for the careful runs.
<cjwatson> indeed.