Add ctest for google unittests

[mariadb-LeonidFedorov]

• RowDecimalTest, ToStringCheck was failing, fixing to current toString output
• deleted utils/rowgroup/rowgroup-tests.cpp as duplicate and never used
• Added ctest with google test and compile_flag WITH_UNITTESTS
• Added compilation and execution for unittests on drone. Unittests shall compile and execute every PR

Example of running tests

ctest -R columnstore                                          
Test project /home/leonid_fedorov_mariadb_com/proj/mdb-server
      Start 49: columnstore:RowDecimalTest.NonNullValueCheck                                     
 1/31 Test #49: columnstore:RowDecimalTest.NonNullValueCheck ...............   Passed    0.02 sec
      Start 50: columnstore:RowDecimalTest.InitToNullAndIsNullValueCheck                         
 2/31 Test #50: columnstore:RowDecimalTest.InitToNullAndIsNullValueCheck ...   Passed    0.02 sec
      Start 51: columnstore:RowDecimalTest.GetBinaryFieldCheck                                   
 3/31 Test #51: columnstore:RowDecimalTest.GetBinaryFieldCheck .............   Passed    0.02 sec
      Start 52: columnstore:RowDecimalTest.ToStringCheck                                         
 4/31 Test #52: columnstore:RowDecimalTest.ToStringCheck ...................   Passed    0.02 sec
      Start 53: columnstore:RowDecimalTest.ToCSVCheck                                            
 5/31 Test #53: columnstore:RowDecimalTest.ToCSVCheck ......................   Passed    0.02 sec
.....
      Start 78: columnstore:CompressionTest.LZ4CanCompress                                       
30/31 Test #78: columnstore:CompressionTest.LZ4CanCompress .................   Passed    0.03 sec
      Start 79: columnstore:CompressionTest.LZvsSnappyUnique                                     
31/31 Test #79: columnstore:CompressionTest.LZvsSnappyUnique ...............   Passed    0.11 sec
                                                                                                          
100% tests passed, 0 tests failed out of 31  

tests can be run in parralel

ctest -j 40 -R columnstore