TST: test fixes for various builds (debian)

TST: json tests to int64 to avoid dtype issues, closes #3895
TST: skip tests if xlrd has lower than needed version, closes #3897
TST: skip pickle tests on not-little endianess , closes #3894
TST: skip test_encoding on non-little endian in test_pytables , closes #3892
TST: skip some stata tests on non-little endian, #3896