[#174,!414] Cleaned up fractional seconds handling

[#174,!414] Cleaned up fractional seconds handling

src/hooks/dhcp/high_availability/communication_state.*
    CommunicationState::logFormatClockSkew() - generates log
    without fractional seconds

src/hooks/dhcp/high_availability/tests/communication_state_unittest.cc
    TEST_F(CommunicationStateTest, logFormatClockSkew)  -
    added check of entire log content

src/lib/http/date_time.*
    HttpDateTime::HttpDateTime() now uses second_clock to eliminate
    fractional seconds

src/lib/util/boost_time_utils.*
    ptimeToText()
    durationToText() - added fsecs_precision parameter to control
    fractional seconds emission

src/lib/util/tests/boost_time_utils_unittest.cc
    TEST(BoostTimeUtilsTest, epoch)
    TEST(BoostTimeUtilsTest, bastilleDay) - revamped to test precision