[#964,!577] Added unit tests

[#964,!577] Added unit tests

src/lib/dhcp/tests/iface_mgr_unittest.cc
    Modified tests to verify that external socket callbacks receive
    the correct socket descriptor when invoked by IfaceMgr.

src/lib/http/tests/server_client_unittests.cc
    TEST_F(HttpClientTest, closeIfOutOfBandwidth) - new test to
    verifies HttpClient::closeIfOutOfBandwidth()