By Nidal al-Mughrabi and Jeffrey Heller GAZA/JERUSALEM, Nov 21 (Reuters) - Israel and Hamas agreed on Wednesday to a ceasefire brokered by Egypt on the eighth day of intensive Israeli fire on the Gaza Strip and militant rocket attacks out of the enclave, Israeli, Palestinian and Egyptian sources said. First word of the truce came from a Palestinian official who has knowledge of the negotiations in Cairo, where U.S.