ENH: Handle passing in coverage command

Source/CTest/cmCTestCoverageCommand.cxx

@@ -71,6 +71,9 @@ bool cmCTestCoverageCommand::InitialPass(
     m_CTest->SetCTestConfiguration("BuildDirectory", build_dir);
     }
 
+  m_CTest->SetCTestConfigurationFromCMakeVariable(m_Makefile,
+    "CoverageCommand", "CTEST_COVERAGE_COMMAND");
+
   cmCTestGenericHandler* handler = m_CTest->GetHandler("coverage");
   if ( !handler )
     {