skel: fix regression in billing properties affecting dcache database commands

The elimination of scoping and db.* properties did not take into account the ability to run the billing cell without a database.  The properties before this change relied on setting db.name and db.schema.changeset conditionally, based on the value of billing.enable.db, so that the dcache database commands would work correctly.

Specifically, when billing db is disabled, dcache database ls should not report the presence of the billing database, and more importantly, dcache database update should not attempt to run the liquibase changesets (since there may be no billing database present at all).

This patch restores the correct behavior.

Testing done:

Before the patch, with billing.enable.db=false,

dcache database ls was still reporting the presence of the database
dcache database update would fail if there is no billing database in the postgres installation (which is quite possible).

After the patch, correct behavior is observed for these commands.

Target: master
Require-notes: yes
Require-book: no
Acked-by: Paul

RELEASE NOTES:

If overriding the database name for billing, be aware that billing.enable.db will not affect the dcache database commands; in particular, update will still attempt to run liquibase.
Thus any non-default setting for this property will require the actual presence of a database by that name.