Sorting by indirect attributes doesn't work

[pcoccoli]

Describe the bug
Sort order is lost in DISP for indirect attributes

Details of the bug

p = GET process
    FROM file:///home/pcoccoli/github/kestrel-lang/test-data/doctored-1k.json
    WHERE name in ('conhost.exe', 'services.exe', 'taskhost.exe')
DISP p ATTR binary_ref.name SORT BY binary_ref.name DESC
sp = SORT p BY binary_ref.name DESC
DISP sp ATTR binary_ref.name

The two DISP outputs do not match - the first is sorted correctly; the second is not.

To Reproduce
Run the statements above

Expected behavior
The two DISP outputs should be the same - sorted descending.

Screenshots

binary_ref.name
   taskhost.exe
   services.exe
    conhost.exe

binary_ref.name
   services.exe
    conhost.exe
   taskhost.exe

[SUMMARY] block executed in 1 seconds
VARIABLE    TYPE  #(ENTITIES)  #(RECORDS)  directory*  file*  process*  user-account*
       p process            9           9           8     16        23              8
      sp process            9           9           0      0         0              0
*Number of related records cached.

[pcoccoli]

There are at least 2 places where we have an issue:

1. firepit's lookup function (used by kestrel in Session.get_variable() via variable.get_entities(). This probably has to be fixed in firepit itself.
2. DISP itself, more specifically the _build_query() private function it uses loses the sort order.