db_test: set timezone to work around mktime bug

Apply workaround for db_test failure on ubuntu 19.04 in OBS. When the
timezone is set to UTC (default in OBS), and the glibc version is 2.29,
the test case is failing sometimes (not always) with the following
errors in the test log:

DAUC Cannot convert LU timestamp '2019-05-26 03:05:03' to time_t: Value too large for defined

Force the timezone to be CET when running the test, so it passes again.
I found this workaround in a Fedora bugreport [1], and tested with an
ubuntu 19.04 system running in docker, that setting the environment
variable like this makes the test pass 25 times in a row. Without it, it
fails every two or three times. Then I verified in my OBS namespace,
that the test also passes in OBS again.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1653340

Related: OS#4026
Change-Id: Ic8080ba1914bb364169ab0c563b132a4ab9a9aab
1 file changed