Removed use of Option::toText from tests:

src/lib/dhcpsrv/tests/cfg_option_unittest.cc
    TEST_F(CfgOptionTest, replace)
    TEST_F(CfgOptionTest, mergeTo)
    TEST_F(CfgOptionTest, createDescriptorOptionValid)

src/lib/dhcpsrv/tests/cfg_subnets4_unittest.cc
    TEST(CfgSubnets4Test, mergeSubnets)