util/hash: Silence comparison between signed and unsigned integer warnings in tests

util/hash: Silence comparison between signed and unsigned integer warnings in tests

delete_management.c:56:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (i = 0; i < size; i++) {
                  ^
delete_management.c:69:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (i = size - 100; i < size; i++) {
                           ^
delete_management.c:79:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
       assert(key_value(entry->key) >= size - 100 &&
                               ^
delete_management.c:79:70: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
       assert(key_value(entry->key) >= size - 100 &&
                                                                      ^
insert_many.c:56:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (i = 0; i < size; i++) {
                  ^
insert_many.c:62:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (i = 0; i < size; i++) {
                  ^
insert_many.c:67:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    assert(ht->entries == size);
                  ^
random_entry.c:62:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (i = 0; i < size; i++) {
                  ^

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>