Change scope of Connection/Statement in test to prevent random failures

[cheenamalhotra]

Test fails randomly due to shared objects in tests which get closed due to race conditions.
This PR makes sure Connection and Statement are always dedicated and open while executing a single test.

[codecov-io]

Codecov Report

Merging #862 into dev will increase coverage by 0.06%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                dev     #862      +/-   ##
============================================
+ Coverage     48.67%   48.74%   +0.06%     
- Complexity     2793     2804      +11     
============================================
  Files           116      116              
  Lines         27875    27877       +2     
  Branches       4650     4650              
============================================
+ Hits          13569    13589      +20     
+ Misses        12099    12087      -12     
+ Partials       2207     2201       -6

Flag	Coverage Δ	Complexity Δ
#JDBC42	48.3% <ø> (+0.14%)	2762 <ø> (+14)	⬆️
#JDBC43	48.61% <ø> (+0.04%)	2794 <ø> (+3)	⬆️

Impacted Files	Coverage Δ	Complexity Δ
...rc/main/java/com/microsoft/sqlserver/jdbc/DDC.java	44.2% <0%> (-1.76%)	107% <0%> (ø)
...soft/sqlserver/jdbc/SQLServerDatabaseMetaData.java	34.84% <0%> (-0.08%)	66% <0%> (ø)
...oft/sqlserver/jdbc/SQLServerParameterMetaData.java	24.56% <0%> (-0.06%)	31% <0%> (ø)
...n/java/com/microsoft/sqlserver/jdbc/Parameter.java	64.32% <0%> (ø)	64% <0%> (ø)	⬇️
...in/java/com/microsoft/sqlserver/jdbc/IOBuffer.java	56.17% <0%> (+0.01%)	0% <0%> (ø)	⬇️
...m/microsoft/sqlserver/jdbc/SQLServerStatement.java	59.57% <0%> (+0.05%)	135% <0%> (ø)	⬇️
...om/microsoft/sqlserver/jdbc/SQLServerBulkCopy.java	52.97% <0%> (+0.17%)	264% <0%> (+1%)	⬆️
...n/java/com/microsoft/sqlserver/jdbc/DataTypes.java	79.48% <0%> (+0.19%)	5% <0%> (+1%)	⬆️
...m/microsoft/sqlserver/jdbc/SQLServerResultSet.java	33.11% <0%> (+0.42%)	260% <0%> (+5%)	⬆️
...c/main/java/com/microsoft/sqlserver/jdbc/Util.java	61.42% <0%> (+0.43%)	90% <0%> (+1%)	⬆️
... and 3 more

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