janus-gateway: make recordplay plugin optional

janus-gateway: make recordplay plugin optional

Currently janus-gateway is built by default with the record and play plugin.
This causes a example config file to be placed on the target filing system
that the user may not need or want, creates a 68K .so
file on the target directory, and janus will also create a warning when ran
if the plugin does not have a matching configuration file setup by the user,
as it will not use the example config file by default.

This patch makes the record and play plugin a option.

Signed-off-by: Adam Duskett <aduskett@codeblue.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>