Due to misc bugs in the way older versions of the gnocchi packages
installed the api-paste.ini, this file is not treated as a dpkg
configuration file, and as a result @ Queens, the file from the
package is not installed over any previous version.

Include api-paste.ini as part of the charm to ensure that a good
paste configuration is installed for all Gnocchi releases.

Change-Id: I1362a64368f0df8e07c7d29d5b504edaf96a70de
Closes-Bug: 1781468