[Halld-offline] Changing the default CCDB source on the farm

[Mark Ito]

The change described below should be transparent to users, and its 
effect will only be felt by some jobs running on the JLab farm. It is 
going into effect sometime this afternoon. If you are interested in the 
details, read on...

For those of you who use gxenv (aka gluex_env_jlab.(c)sh) the source of 
your CCDB information is set by the script 
$BUILD_SCRIPTS/calib_url_chooser.sh. On the farm, you get one of 100 
copies of the SQLite version of the CCDB, chosen randomly, otherwise you 
use our standard database server, hallddb.jlab.org, to get CCDB 
constants. This scheme was described in a previous email 
<https://mailman.jlab.org/pipermail/halld-offline/2019-April/003613.html>.

This behavior is going to change this afternoon.

To move traffic to the new mysql server, hallddb-farm.jlab.org, it will 
now be chosen to serve CCDB constants when on the farm. Non-farm jobs 
will be directed to hallddb.jlab.org as before. The new server was 
described in another previous email 
<https://mailman.jlab.org/pipermail/halld-offline/2019-September/003758.html>.

If you don't use gxenv or calib_url_chooser.sh, then this change does 
not affect you.

If you would like to use the random SQL file scheme (the previous 
default on the farm), you can give an option to the chooser script:

    export JANA_CALIB_URL=`$BUILD_SCRIPTS/calib_url_chooser.sh sqlite`

This choice will be honored whether you are on the farm or not.

Finally, note that if we run into trouble with this change, it is easy 
to reverse.

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