Fix test failures on pre-2016 servers

[gordthompson]

Replace DROP TABLE IF EXISTS calls for compatibility with pre-2016 servers. ( Issue #214 )

[codecov-io]

Codecov Report

Merging #215 into dev will increase coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                dev     #215      +/-   ##
============================================
+ Coverage     32.82%   32.85%   +0.03%     
  Complexity     1436     1436              
============================================
  Files            97       97              
  Lines         23383    23383              
  Branches       3889     3889              
============================================
+ Hits           7675     7683       +8     
+ Misses        14163    14150      -13     
- Partials       1545     1550       +5

Flag	Coverage Δ	Complexity Δ
#JDBC41	32.74% <ø> (+0.08%)	1432 <ø> (+6)	⬆️
#JDBC42	32.79% <ø> (+0.05%)	1435 <ø> (+1)	⬆️

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/microsoft/sql/DateTimeOffset.java	37.14% <0%> (-2.86%)	8% <0%> (-2%)
...m/microsoft/sqlserver/jdbc/SQLServerResultSet.java	23.84% <0%> (-0.05%)	170% <0%> (ø)
...in/java/com/microsoft/sqlserver/jdbc/IOBuffer.java	36.54% <0%> (+0.2%)	0% <0%> (ø)	⬇️
...om/microsoft/sqlserver/jdbc/SQLServerBulkCopy.java	45.16% <0%> (+0.36%)	183% <0%> (+2%)	⬆️

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[xiangyushawn]

@gordthompson Thank you for your contribution. Now, all the tests succeed against SQL Server 2008 with your fix. Thank you.