populate-archive should ignore arch-all packages

When creating a copy archive for rebuild purposes and its list of architectures doesn't include the nominatedarchindep architecture, it falls over in a big heap. We should make it ignore arch-all packages if the nominatedarchindep is not present on the list of requested arches.

{{{
Traceback (most recent call last):
  File "/srv/launchpad.net/codelines/current/scripts/populate-archive.py", line 22, in <module>
    script.lock_and_run()
  File "/srv/launchpad.net/codelines/soyuz-production-rev-9432/lib/lp/services/scripts/base.py", line 285, in lock_and_run
    implicit_begin=implicit_begin, isolation=isolation)
  File "/srv/launchpad.net/codelines/soyuz-production-rev-9432/lib/lp/services/scripts/base.py", line 243, in run
    self.main()
  File "/srv/launchpad.net/codelines/soyuz-production-rev-9432/lib/lp/soyuz/scripts/ftpmasterbase.py", line 302, in main
    self.mainTask()
  File "/srv/launchpad.net/codelines/soyuz-production-rev-9432/lib/lp/soyuz/scripts/populate_archive.py", line 318, in mainTask
    opts.packageset_delta_flag)
  File "/srv/launchpad.net/codelines/soyuz-production-rev-9432/lib/lp/soyuz/scripts/populate_archive.py", line 269, in populateArchive
    proc_families)
  File "/srv/launchpad.net/codelines/soyuz-production-rev-9432/lib/lp/soyuz/scripts/populate_archive.py", line 430, in _createMissingBuilds
    architectures_available=architectures, logger=self.logger)
  File "/srv/launchpad.net/codelines/soyuz-production-rev-9432/lib/lp/soyuz/model/publishing.py", line 546, in createMissingBuilds
    self, architectures_available, self.distroseries, pas_verify)
  File "/srv/launchpad.net/codelines/soyuz-production-rev-9432/lib/lp/soyuz/pas.py", line 177, in determineArchitecturesToBuild
    ' '.join(legal_arch_tags))
AssertionError: nominatedarchindep is not present in legal_archseries: armel
}}}