Add default label and mapping for vendor services

Adding the default label/mapping is important because:
1.  Lookups of services without an selinux label should generate
    a denial.
2.  In permissive mode, lookups of a service without a label should be
    be allowed, without the default label service manager disallows
    access.
3.  We can neverallow use of the default label.

Bug: 37762790
Test: Build and flash policy onto Marlin with unlabeled vendor services.
    Add/find of unlabeled vendor services generate a denial.

Change-Id: I66531deedc3f9b79616f5d0681c87ed66aca5b80