Add preparer to pymssql that disables percent doubling

Add preparer to pymssql that disables percent doubling

Fixed the pymssql dialect so that percent signs in SQL text, such
as used in modulus expressions or literal textual values, are
**not** doubled up, as seems to be what pymssql expects.  This is
despite the fact that the pymssql DBAPI uses the "pyformat" parameter
style which itself considers the percent sign to be significant.

Tests are part of standard suite already (CI has been disabled)

Change-Id: Ie05de403caefcba3292a967183a995e95a5854d5
Fixes: #4057