[#484] Expands supported hex literal formats in option data

[#484] Expands supported hex literal formats in option data

src/bin/dhcp4/tests/config_parser_unittest.cc
    TEST_F(Dhcp4ParserTest, optionDataInvalidHexLiterals)
    TEST_F(Dhcp4ParserTest, optionDataValidHexLiterals) - new tests

src/bin/dhcp6/tests/config_parser_unittest.cc
    TEST_F(Dhcp6ParserTest, optionDataInvalidHexLiterals)
    TEST_F(Dhcp6ParserTest, optionDataValidHexLiterals) - new tests

src/lib/dhcpsrv/parsers/option_data_parser.*
    OptionDataParser::createOption() - modified to use
    util::str::decodeFormattedHexString()

src/lib/dhcpsrv/tests/dhcp_parsers_unittest.cc
    TEST_F(ParseConfigTest, hexOptionData) - new test

src/lib/util/strutil.*
    decodeSeparatedHexString() - new function which accepts
    the octet separator as a parameter

    decodeFormattedHexString() - now detects either colons or
    or spaces as octet separators