Use package-installs in more elements

Updates additional elements in diskimage-builder to use the declarative
package install support provided by the package-installs element.
package-installs does not yet support the pkg-map functionality, so
elements using pkg-map are not migrated. That support will come in the
near future.

Change-Id: I3d36adad317ba44326eabd95243d45807e2a8a16
Merge "Use package-installs in more elements"