This test always generate a random string so each time the test is run we will
test the hash function with a new value.
It also hashes the same string twice and compares the result so that we have a
chance of catching if uninitialized variables are getting mixed into the value
calculation and end up generating different results for the same input.

Removed:
    SSS_UNRESOLVED_DEBUG_LEVEL (completely replaced with SSSDBG_UNRESOLVED)

Added new macro:
    CONVERT_AND_SET_DEBUG_LEVEL(new_value)

Changes unresolved debug level value (SSSDBG_UNRESOLVED) from -1 to 0
so DEBUG macro could be reduced by one condition. Anyway, it has a minor
effect, every time you want to load debug_level from command line parameters,
you have to use following pattern:

    /* Set debug level to invalid value so we can deside if -d 0 was used. */
    debug_level = SSSDBG_INVALID;

    pc = poptGetContext(argv[0], argc, argv, long_options, 0);
    while((opt = poptGetNextOpt(pc)) != -1) { ... }

    CONVERT_AND_SET_DEBUG_LEVEL(debug_level);

https://fedorahosted.org/sssd/ticket/925

Conversion of the old debug_level format to the new one.
(only where it was necessary)

Removed:
  SSS_DEFAULT_DEBUG_LEVEL (completely replaced with SSSDBG_DEFAULT)

Specially crafted packages might lead to an integer overflow and the
parsing of the input buffer might not continue as expected. This issue
was identified by Sebastian Krahmer <krahmer@suse.de>.

Also adds a unit test.