Reinstate "services: Add a service for Jami."

Reinstate "services: Add a service for Jami."

This reverts commit 4673f817938d9d2b1b40a072ab2e0c44a32ccc97, which reverted
commit 69dcc24c9f0cdfea674eb690e7755d26a25ced2b with the fix detailed below.

Thanks to Christopher Baines for reporting the failure and proposing a fix.

* guix/self.scm (compiled-guix) [*system-test-modules*]: Add the test data
files via the 'extra-files' argument.
* gnu/local.mk (dist_patch_DATA): Move the tests/data/jami-dummy-account.dat
file to...
* gnu/local.mk (MODULES_NOT_COMPILED): ... here.