Is the "glass nose" Tu-134 design for easier conversion to military use?
Converting a Tu-104, a Tu-124 or a Tu-134 to a bomber only would had worked if there had also been provisions for a bomb bay. Including this in a pressurized fuselage would had incurred a severe weight penalty, so there was no easy way for a bomber conversion. This should make the speculation about dual use as a bomber moot.

However, there are several good reasons to use the glazed nose:


Easier conversion of trained bomber crews (trained on the Il-28 and Tu-16) for civilian duties. Remember that the Tu-104 was the second jet airliner in service and the only operational jet airliner worldwide between 1956 and 1958.
Operation as a military transport on improvised flights (where the better view of the navigator in the nose would help in visual navigation).
Civilian operation on flights on routes without navigation aids.


The last point is added by @JanHudec as a comment to this answer, but would exclude the operation on a scheduled service, because the aircraft would not be able to navigate in fog or at night.

Since the glazed nose was removed quite early in the production run of the Tu-134 (from the A-2 version on), it seems that the first reason (dual use of Tu-16-trained crews) is the most likely. While more than 1,500 Tu-16s were built, the Tu-104 (201 built from 1956 to 1960) and Tu-124 (164 built from 1960 to 1965) were relatively rare. From the Wikipedia page on the Tu-104:


  Pilots with previous Tu-16 experience transitioned into the Tu-104
  with relative ease