Also use MockSystemReader in GitDateParserBadlyFormattedTest
All tests should use MockSystemReader to isolate them from the
underlying platform specifics.
GitDateParserBadlyFormattedTest wasn't using MockSystemReader which
induced Bug 420772 as a side effect since GitDateParser caches
SimpleDateFormat instances without regarding their locale. This will be
fixed in another change
Bug: 420772
Change-Id: I798e55d05730a71bb0326f80aea5488541d6c1f2 Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>