the validate_legacy function is marked for deprecation in
v9.0.0 from puppetlabs-stdlib.
Note that this change removes the pattern validation about [DEFAULT]
pipeline. The existing pattern check is incomplete, because of
the following two reasons.
- the pattern does not guarantee that the requested pipeline is
really supported or not
- the pattern accepts a+b+c but the existing pipelines in glance
does not have any entries with this pattern
Change-Id: I156d9a3a30ba6c523a0b16a14bf8a1839b61fb78