[evlatests] setting reference antennas

[Ken Sowinski]

By default telcal chooses, for any subarray, the antenna with the
smallest DCS number as the reference antenna.  This is not always
desirable.  That antenna may be broken; for a phased array observation
another antenna might be more appropriate.

I have placed a script 'setrefant' in /home/mchost/evla/bin which
uses the long-ago-implemented REST interface to the PhysicalAntenna
to set a reference antenna or antennas.  The choice remains in place
for the duration of the scrupt currently executing.  If a new script
is started another reference antenna choice will need to be made.

Examples:
To force antenna 13 to be the reference antenna,
setrefant ea13

To forcer antennas 14 and 15 to be reference antennas,
setrefant "ea14 va15"

Caveat:
It has been a long time since I tested that telcal really responds
to explicit reference antenna choices.  Some careful checking is
encouraged.