Clean up harness helper functions for programs and kernels

[bashbaug]

See: #2595 (review)

Our current harness functions for programs and kernels are confusing. We should clean them up to simplify development and maintenance in the future.

Some specific suggestions:

1. The harness function create_single_kernel_helper_create_program_for_device is never used and can be removed.
2. The harness function create_single_kernel_helper_with_build_options just calls the harness function create_single_kernel_helper. We should remove create_single_kernel_helper_with_build_options and just call create_single_kernel_helper directly, instead.
3. There are two overloads of create_single_kernel_helper_create_program: one is a version called directly by tests and another is an internal helper function only used within the harness. We should name the functions differently to disambiguate their uses.
4. Build options are handled subtly differently in create_single_kernel_helper and create_single_kernel_helper_create_program: in create_single_kernel_helper, the build options are modified to add the highest supported OpenCL C version supported by all device in the context (assuming no other OpenCL C version is specified explicitly), whereas in create_single_kernel_helper_create_program the build options are left unmodified. Is this intentional? If so, we should find a way to make this difference clear.

It would be fine to do this cleanup in multiple steps, since (1), (2), and (3) are fairly straightforward, whereas (4) may require more thought and discussion.

[shajder]

Few additional remarks:

1. from std::string get_kernel_name(const std::string &source) removed additional kernelsList[kernelsList.size() - 1] = '.';

2. in is_image_format_supported num_entries parameters value for clGetSupportedImageFormats function shoudln't be 128, replaced with 0

3. Would that work correctly for multi-context test ?

size_t get_min_alignment(cl_context context)
{
    static cl_uint align_size = 0;

    if (0 == align_size)
    {
    ...