[evlatests] New level setting algorithm

[Ken Sowinski]

As of December 5 we have executor and MIB software in place to
try to get T304 attenutors set more quickly at a band change.

The old way was to slew first the input attenuator to the
desired set point at 1 dB per second and then the output
attenuator.  The new MIB algorithm bumps the attenuator by
the difference between the current and desired power measuremnt
and then, if necessary, will slew at 1 dB per second to the
desired setting.  In addition the effective time for the
levelsetting command allows time for the subreflecor to move
to a new position so that the ALC loop does not work on an
erroneous wrong power measurement.

The ALC algortihm described is used for IFs A and C.  B and D
still are set from a band dependent table.

T_sys behavior at a band change should be interpreted with these
changes in mind.