Fix reading time format

[janikn67]

Current nzpy implementation is not adjusted to include microseconds while reading time type and Netezza supports time type with microseconds resolution from 00:00:00.000000 to 23:59:59.999999. When microseconds are equal to 0, they are not displayed:

SYSTEM.ADMIN(ADMIN)=> select * from test_time;
      TIME       
-----------------
 01:00:01
 01:02:03.004005
 00:00:00
 23:59:59.999999
(4 rows)

SYSTEM.ADMIN(ADMIN)=> insert into test_time values ('12:30:30.000000');
INSERT 0 1
SYSTEM.ADMIN(ADMIN)=> select * from test_time;
      TIME       
-----------------
 01:00:01
 01:02:03.004005
 00:00:00
 23:59:59.999999
 12:30:30
(5 rows)

Provided fix adds microseconds to the time and adjusts the display depending on their value.

Testing:

• most of the tests passed - observed ERROR: Function 'XMLPARSE(UNKNOWN)' does not exist but it seems unrelated
• fixed some tests cases in test_functional.py