By Michelle Nichols, Nidal al-Mughrabi and Dan Williams UNITED NATIONS/CAIRO/JERUSALEM (Reuters) -The U.N. Security Council called for boosting humanitarian assistance for Gaza, but the U.N. chief said the way Israel was conducting its military operation was creating “massive obstacles” to aid distribution inside the battered enclave. After days of wrangling to avert a threatened U.S. veto, the Security Council on Friday passed a resolution urging steps to allow “safe, unhindered, and expanded humanitarian access” to Gaza and “conditions for a sustainable cessation” of fighting. The resolution…