Fix write failure on PDP statistics

Fix write failure on PDP statistics

Due to the precision of time stamps being saved to the nearest second,
a millisecond precision timestamp was being compared to a second
precision timestamp, causing the write to fail. This change fixes that.

A unit test is also added to test for this on the provider.

In addition, a USE-MARIADB flag is being introduced, which allows unit
tests to be run against a locally installed MariaDB instance so that the
unit tests can be verified against MariaDB locally rather than H2, the
default in Gerrit.

Issue-ID: POLICY-3146
Change-Id: I878f160956e89506743dc074679ee81ac1c48216
Signed-off-by: liamfallon <liam.fallon@est.tech>
(cherry picked from commit d6db5582b6705c11abbf8b507aa423aa00bcd7ae)