stack/erp5: Fix path-based routing when there are multiple components in the outer prefix.

The _vh_ prefix is needed for every single outer path element for
VirtualHostMonster to be able to properly reconstruct the outer path.
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Status Job ID Name Coverage
  External
passed SlapOS.SlapRunner.ResilienceTest-Master

00:26:20

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:22:27

passed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

05:31:11

passed SlapOS.SlapRunner.ResilienceTest-Master

00:27:51