Refactor wimpy feature (#2507)

- Make it a common parameter in harness using either '-w', '--wimpy' or
'CL_WIMPY_MODE' environment variable.
- Remove all test specific wimpy variable.

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Co-authored-by: Kévin Petit <kpet@free.fr>

test_conformance/half/cl_utils.h

@@ -74,7 +74,6 @@ extern bool gHostReset;
 // gWimpyMode indicates if we run the test in wimpy mode where we limit the
 // size of 32 bit ranges to a much smaller set.  This is meant to be used
 // as a smoke test
-extern bool gWimpyMode;
 extern int gWimpyReductionFactor;
 
 uint64_t ReadTime( void );