test_cross_engine_read_write_netcdf4 is broken on Python 3 due to some sort of upstream change

[shoyer]

This has started causing test failures on master.

I had trouble tracking this down, but it seems to be related to a build of hdf5, netCDF4 or the underlying libraries which just became available on conda.

In case anyone else has time for it:
This build worked: https://travis-ci.org/xray/xray/jobs/75633366
This build failed: https://travis-ci.org/xray/xray/jobs/75777788

For now, let's just skip the test and come back to this later.

Possibly related: Unidata/netcdf4-python#448

[jhamman]

Here's a diff of the versions that went into each build environment:

$ diff -y worked.txt broken.txt
 curl: 7.38.0-0 | curl: 7.43.0-1 
 hdf5: 1.8.14-0 | hdf5: 1.8.15.1-1 
 libnetcdf: 4.3.2-1 | krb5: 1.13.2-0 
 netcdf4: 1.1.8-np19py34_0 | libnetcdf: 4.3.3.1-1 
 > netcdf4: 1.1.9-np19py34_0 

given that the failure is in an I/O test, it seems likely that this is coming from netcdf4.

[QuLogic]

See #1298, where I changed Python 2.7 CI to install h5netcdf as well (it seemed to be missing.) This test doesn't work on Python 2 either right now.