[3360] Fix Memfile config string for Dhcp4 srv unit tests.

src/bin/dhcp4/tests/dhcp4_test_utils.h

@@ -117,7 +117,8 @@ public:
     /// @param port port number to listen on; the default value 0 indicates
     /// that sockets should not be opened.
     NakedDhcpv4Srv(uint16_t port = 0)
-        : Dhcpv4Srv(port, "type=memfile", false, false) {
+        : Dhcpv4Srv(port, "type=memfile universe=4 persist=false",
+                    false, false) {
         // Create fixed server id.
         server_id_.reset(new Option4AddrLst(DHO_DHCP_SERVER_IDENTIFIER,
                                             asiolink::IOAddress("192.0.3.1")));

src/bin/dhcp6/tests/dhcp6_test_utils.h

@@ -45,7 +45,7 @@ class NakedDhcpv6Srv: public isc::dhcp::Dhcpv6Srv {
 public:
     NakedDhcpv6Srv(uint16_t port) : isc::dhcp::Dhcpv6Srv(port) {
         // Open the "memfile" database for leases
-        std::string memfile = "type=memfile universe=6";
+        std::string memfile = "type=memfile universe=6 persist=false";
         isc::dhcp::LeaseMgrFactory::create(memfile);
     }