Timestamp tests flaky under autopkgtest infrastructure

Here's the relevant section of the log:

********* Start testing of TestToken *********
Config: Using QtTest library 5.5.1, Qt 5.5.1 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 5.3.1 20160519)
PASS : TestToken::initTestCase()
PASS : TestToken::testEmptyToken()
PASS : TestToken::testTokenEmptyStrings()
PASS : TestToken::testTokenArgs()
PASS : TestToken::testTokenCopy()
PASS : TestToken::testToQuery()
PASS : TestToken::testFromQuery()
PASS : TestToken::testTokenName()
QWARN : TestToken::testSignUrlEmpty() Unable to sign empty URL.
PASS : TestToken::testSignUrlEmpty()
QWARN : TestToken::testSignUrl() No main loop, defaulting to local timestamp.
PASS : TestToken::testSignUrl()
QWARN : TestToken::testGetServerTimestamp() No main loop, defaulting to local timestamp.
PASS : TestToken::testGetServerTimestamp()
QDEBUG : TestToken::testGetServerTimestampMuchEarlier() Getting timestamp from server: "http://localhost:8000/muchearlier"
QSYSTEM: TestToken::testGetServerTimestampMuchEarlier() Error fetching server timestamp: ""
QDEBUG : TestToken::testGetServerTimestampMuchEarlier() Got server timestamp: 4294967295
FAIL! : TestToken::testGetServerTimestampMuchEarlier() Compared values are not the same
   Actual (result.toTime_t()): 4294967295
   Expected ((uint)864016336) : 864016336
   Loc: [/tmp/autopkgtest.8ZVzC7/build.D0s/ubuntuone-credentials-15.11+16.10.20160608/libubuntuoneauth/tests/test_token.cpp(167)]
QDEBUG : TestToken::testGetServerTimestampMuchLater() Getting timestamp from server: "http://localhost:8000/muchlater"
QSYSTEM: TestToken::testGetServerTimestampMuchLater() Error fetching server timestamp: ""
FAIL! : TestToken::testGetServerTimestampMuchLater() Compared values are not the same
   Actual (result.toTime_t()): 1466036448
   Expected ((uint)1283465647) : 1283465647
   Loc: [/tmp/autopkgtest.8ZVzC7/build.D0s/ubuntuone-credentials-15.11+16.10.20160608/libubuntuoneauth/tests/test_token.cpp(204)]
PASS : TestToken::testTimesCached()
PASS : TestToken::testCreatedParsed()
PASS : TestToken::testUpdatedParsed()
PASS : TestToken::testCreatedMissing()
PASS : TestToken::testUpdatedMissing()
PASS : TestToken::testNewWithDates()
PASS : TestToken::testSSODateToISO()
PASS : TestToken::testISODateToISO()
PASS : TestToken::cleanupTestCase()
Totals: 20 passed, 2 failed, 0 skipped, 0 blacklisted

Full log is attached