Fix SSO with instance name instead of port

[Ununnilium]

When a named instance instead of a port is used, Kerberos logins failed because the spn string was "MSSQLSvc@SERVER_NAME:None" instead of "MSSQLSvc@SERVER_NAME:INSTANCE_NAME". When "port" is None (parsed_servers[0][1]), "instance" (parsed_servers[0][2]) should be used.

[codecov[bot]]

Codecov Report

Merging #129 (53424af) into master (7c73812) will decrease coverage by 1.79%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #129      +/-   ##
==========================================
- Coverage   93.58%   91.79%   -1.80%     
==========================================
  Files          28       27       -1     
  Lines        7947     7736     -211     
==========================================
- Hits         7437     7101     -336     
- Misses        510      635     +125     

Impacted Files	Coverage Δ
src/pytds/__init__.py	91.49% <100.00%> (-0.94%)	:arrow_down:
src/pytds/tls.py	18.64% <0.00%> (-74.58%)	:arrow_down:
tests/fixtures.py	93.33% <0.00%> (-6.67%)	:arrow_down:
tests/unit_test.py	94.10% <0.00%> (-4.98%)	:arrow_down:
tests/utils.py	81.13% <0.00%> (-1.89%)	:arrow_down:
src/pytds/tds_base.py	93.65% <0.00%> (-1.47%)	:arrow_down:
src/pytds/tds.py	95.90% <0.00%> (-0.63%)	:arrow_down:
tests/connected_test.py	97.53% <0.00%> (-0.62%)	:arrow_down:
tests/all_test.py	94.92% <0.00%> (-0.14%)	:arrow_down:
... and 2 more

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[denisenkom]

Why do you need to use socket.getfqdn, you did not explain that in the description