bpo-30822: Exclude tzdata from regrtest --all (#2775)

bpo-30822: Exclude tzdata from regrtest --all (#2775)

When running the test suite using --use=all / -u all, exclude tzdata
since it makes test_datetime too slow (15-20 min on some buildbots)
which then times out on some buildbots.

-u tzdata must now be enabled explicitly, -u tzdata or -u all,tzdata,
to run all test_datetime tests.

Fix also regrtest command line parser to allow passing -u
extralargefile to run test_zipfile64.

Travis CI: remove -tzdata. Replace -u all,-tzdata,-cpu with -u all,-cpu since tzdata is now excluded from -u all.