[iquery] Refactor iquery to use new reader interface

This change replaces iquery's manual traversal code with the new
inspect/reader.h interface.

To simplify iquery path handling and to make parts of the path more
clear, this change also introduces a delimiter between the file part and
inspect part of a particular path.

Consider the inspect tree:
objects:
 table-0x0:
  row-0x1:
 table-0x2:

Previously we would write:
$ iquery --ls --full_paths objects/table-0x0
objects/table-0x0/row-0x1

Now we write:
$ iquery --ls --full_paths objects#table-0x0
objects#table-0x0/row-0x1

The delimiter '#' separates the file part of the path from the inspect
part, which makes the meaning more clear ("open inspect at this
location, then traverse to this child" vs. "expect to find an inspect
endpoint along this path and once that is open continue traversing to
the proper location").

CF-218: #progress

Change-Id: I31df97351aca4e3df5f53df4aa842c7207c2e18d