Add tests for cynara_admin_erase

Add tests for cynara_admin_erase

All tests try erasing policies in different scenarios and then verify
if proper policies were removed from proper buckets, but listing what
is left and comparing to expected result.

There are 7 tests added:
* tc23_admin_erase_empty_bucket - erase policies from empty bucket;
* tc24_admin_erase_no_bucket - try to erase from not existing bucket;
* tc25_admin_erase_single_bucket - check all posibilities of matching
 policies during erase;
* tc26_admin_erase_recursive_not_linked_buckets - erase with recursive
 flag set to TRUE, but in case where no policy lead to subbucket;
* tc27_admin_erase_recursive_linked_buckets - erase with recursive flag
 set to TRUE with existance of policy leading to subbucket;
* tc28_admin_erase_non_recursive_linked_buckets - erase with recursive
 flag set to FALSE with existance of policy leading to subbucket;
* tc29_admin_erase_recursive_from_sub_bucket - start erase test in
 subbucket and check if parent bucket stays unaffected by erase.

Change-Id: Ib712a028d97773e70b98de85c51aff0238bb8586