Correctly handle INT UNSIGNED column types.

[rulle-io]

Fix for #294 , where dbeam cannot handle UNSIGNED INT column type values more than INTEGER.MAX_VALUE (2147483647L).

It seems like the most appropriate property to select correct Avro type is to use ResultSetMetaData.getColumnClassName() method.

Tests

• "Unit tests included"
• "I successfully ran my jobs with this code"

Checklist for PR author(s)

• Changes are covered by unit tests (no major decrease in code coverage %) and/or integration tests.
• Ensure code formating (use mvn com.coveo:fmt-maven-plugin:format org.codehaus.mojo:license-maven-plugin:update-file-header)
• Document any relevant additions/changes in the appropriate spot in javadocs/docs/README.

[codecov]

Codecov Report

Merging #380 (f22e21f) into master (2315e22) will increase coverage by 0.15%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #380      +/-   ##
============================================
+ Coverage     91.42%   91.57%   +0.15%     
- Complexity      241      244       +3     
============================================
  Files            26       26              
  Lines           921      938      +17     
  Branches         65       69       +4     
============================================
+ Hits            842      859      +17     
  Misses           52       52              
  Partials         27       27              

[rulle-io]

@labianchin

[rulle-io]

Closes #294 .