Fix regression when reflecting tables in MSSQL

Fix regression when reflecting tables in MSSQL

Fix a regression introduced by the reflection of computed column in
MSSQL when using SQL server versions before 2012, which does not support
the ``concat`` function and when using the legacy TDS version 4.2.
The dialect will try to detect the protocol version of first connect
and run in compatibility mode if it cannot detect it.

Fixes: #5255
Fixes: #5271
Change-Id: I7b33f7889ac0784cd8ae5385cbd50bc8c862398a