Configure test fixture using CTest for Windows build

- Added new test/test_suite.in with list of regression and unit tests
  previously in Makefile.am, to be shared between Unix and Windows
  builds.
- Updated regression.cc & unit.cc to return the number of failed tests
  to indicate to CTest that the test failed. Similarly, a crash or
  unhandled exception terminates the process with a non-zero exit code.
  - This change doesn't affect running the tests with autotest in Unix
    builds because this processes test output from custom-test-driver &
    test-suite.sh, and ignores the exit code of the test runner.
- Removed comment in test/test-cases/regression-offset-variable.json as
  this is not supported by JSON and prevents strict parsers to read and
  process the file.
- Minor change in regression.cc's clearAuditLog to replace std::ifstream
  with std::ofstream as the mode to open the flag applies to an output
  stream.
- Minor change in unit.cc to simplify code that deletes tests.
- Minor changes to test/custom-test-driver to correct usage information.

test/test-cases/regression/offset-variable.json

@@ -215,7 +215,6 @@
       ]
     },
     "expected":{
-      // should not match
     },
     "rules":[
       "SecRequestBodyAccess On",
@@ -248,7 +247,6 @@
       ]
     },
     "expected":{
-      // should not match
     },
     "rules":[
       "SecRequestBodyAccess On",