Refactor mwax_u2s.cfg config file format

[gsleap]

The mwax_u2s.cfg config file which lives on /vulcan/mwax_config/mwax_u2s.cfg looks like this:

mwa@mwax01:~$ cat /vulcan/mwax_config/mwax_u2s.cfg
0,unknown,0,8388608,255,255,255,255,,,,,,,0,,0,127.0.0.1
1,mwax01,0,8388608,255,255,255,255,/dev/shm/mwax,/dev/shm/mwax.temp,/mwax_stats,,/home/mwa/metafits,192.168.90.201,1,239.255.90.1,59001,10.128.21.1
2,mwax02,0,8388608,255,255,255,255,/dev/shm/mwax,/dev/shm/mwax.temp,/mwax_stats,,/home/mwa/metafits,192.168.90.202,2,239.255.90.2,59002,10.128.21.2
3,mwax03,0,8388608,255,255,255,255,/dev/shm/mwax,/dev/shm/mwax.temp,/mwax_stats,,/home/mwa/metafits,192.168.90.203,3,239.255.90.3,59003,10.128.21.3
...

This format is problematic for several reasons:

• Difficult to read and edit. Errors are VERY easy to make.
• Config file is not validated (much) by mwax_u2s.
• Some redundant information. E.g. if coarse channel number is 5, then the multicast address will be 239.255.90.5 and port will be 59005. Perhaps we can reduce the redundant info like this by storing channel 5 in the config file, and mwax_u2s will determine the multicast ip and port in code.
• Lots of common information- e.g. the mwax path (/dev/shm/mwax) and metafits path. Only configure these per host by exception?