Before you install tdsodbc run this:
# Ensure FreeTDS is added to unixodbc upon installation
RUN echo tdsodbc freetds/addtoodbc boolean true | debconf-set-selections
Otherwise the driver will not be automatically added to the list of available drivers without subsequently editing /etc/odbcinst.ini to add:
[FreeTDS]
Description=TDS driver (Sybase/MS SQL)
Driver=libtdsodbc.so
Setup=libtdsS.so
CPTimeout=
CPReuse=
UsageCount=1