The last LU time gets read from the database as string, parsed with
strptime to "struct tm", and then gets converted to time_t with mktime.
A recent behavior change in glibc's mktime implementation unconvered,
that we don't have tm.tm_isdst (daylight saving time) set properly. As
"struct tm" was not initialized, and strptime did not write to tm_isdst,
it was set to a random value. When it was not 0, db_test failed on UTC
systems with a more recent glibc (e.g. Ubuntu 19.04).
Fix this by zero-initializing "struct tm" and remove the previous
workaround that made db_test pass on UTC systems.
Related: OS#4026
Change-Id: Iebbbe42fc5cd43324206d9433ede67b39251389c
Oliver Smith
63de00cfc1