simple-agent: Enable bluetooth technology.

We can't to anything with bluetooth until its enabled via connman
(otherwise everything else will blocked/soft rfkilled).

Enable it explicitely in the agent so the user doesn't have to first use
connmanctl.

Reviewed-by: Philip Withnall <philip.withnall@collabora.co.uk>
Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D2209