Add test cases generator.

Add test cases generator.

    v1:
    File utest_generator.py contain the base class and function for generating
    File utest_math_gen.py can generate most math function for all the gentype
    utest_math_gen.py can be run during cmake.

    v2:
    1. Put all the generated unit test cases to folder utest/generated.
    2. Delete all generated folder while involve make clean.
    3. At the top of the generated test cases, add some comments
    4. Instead of defined FLT_ULP(0.000001) as the ulp unit, caculate the float ulp before using it.
    5. Add several math functions' test case.

    v3:
    1. Refine the calculation for float, and calculate each float got from cpu function.

    v4:
    Refine the calculation for float.

    Following fucntions test cases fail with input 0, 1 or 3.14:
	builtin_atan2_float
	builtin_atanh_float
	builtin_rootn_float
    builtin_cos_float
    builtin_cospi_float
    builtin_erf_float
    builtin_erfc_float
    builtin_mad_float
    builtin_nextafter_float
    builtin_pown_float
    builtin_powr_float
    builtin_rint_float
    builtin_sinpi_float
    builtin_tan_float
    builtin_tanpi_float

    v5:
    remove case builtin_mad_float

	todo:
	atan2pi
	fmax
	fmin
	sincos

Signed-off-by: Yi Sun <yi.sun@intel.com>
Signed-off-by: Yangwei Shui <yangweix.shui@intel.com>
Reviewed-by: Zhigang Gong <zhigang.gong@linux.intel.com>
Reviewed-by: "Song, Ruiling" <ruiling.song@intel.com>