Handle all date/time stamps uniformly, taking in account the host
endianness. Respect the local time zone and the '-Z' option for
all ipmitool commands. Unify the date and time formatting.
Add correct handling of IPMI timestamps 'since system startup'
and for 'unspecified' timestamps.
Partially resolvesipmitool/ipmitool#23
Signed-off-by: Alexander Amelkin <alexander@amelkin.msk.ru>