[mythtv] Changes needed to ansible for Raspberry Pi for mythtv v31

[Peter Bennett]

Hi Stuart

For the raspberry pi (buster) build of V31, some changes are needed, 
extra build dependencies. Please can you add these for raspberry pi. I 
would expect they would also be needed for other environments, perhaps 
that was already done.

These are needed for the python bindings, otherwise the python bindings 
get disabled
python3-lxml
python3-mysqldb
python3-future

This is needed for plugins, otherwise NetMinder gets disabled
libmariadb-dev-compat

NOTE I cannot build Zoneminder, because it is asking for python3-urllib2 
BUT only python3-urllib3 is available.
Zoneminder also wants python3-pycurl and python3-oauth - but until it 
can use urllib3 there is no point in adding these.

For now, Zoneminder is disabled

If somebody sorts out the urllib3 problem, I can fix mythtv-light so 
that zoneminder will be built.

Peter