Make Runtime class aware of modules

Previously there was no way to reference tables in
one policy from another policy.  A table name such
as 'nova:servers' was treated as an opaque string
by the Runtime.  This made it impossible for
policies to share tables.

This change makes the Runtime class aware of the convention.
This way, users can create multiple policies that reference
tables defined in another policy, e.g. when all of the
policies want to share the data exported by datasources
(since those are stored within policies as well).

Note that caution must be used because cycles across
policies will cause an infinite loop.  A subsequent
change will include that safety check.

Implements-blueprint: multiple-policies
Change-Id: I3547f857b3f73f752fa09911933474125ce07d84
Merge "Make Runtime class aware of modules"