Generate per-hashmap random seed with OpenSSL

- Modify SConstruct to link -lcrypto
- Load OpenSSL error strings on startup
- Nuke old init_hashmap_random(); instead we have hashmap_get_random(),
  which takes a pointer to 32-bit uint which will be set to 32 bits of
  random
- hashmap_init() calls hashmap_get_random() to seed new map->seed
  attribute
- Modify hashmap_insert_table() helper to take a seed parameter

CR: gcc, tests