Restore 'grpc' extra for testing on Python 2.7.

[tseaver]

Bump minimum required 'grpc' version to 0.13.1, which supports UCS-4 and UCS-2 builds on Linux.

Closes#1572.

[tseaver]

time .tox/py27/pip install gcloud[grpc] call trades off about one second on my machine, in exchange for some DRYness (maintaining the pinned grpcio version only in setup.py). Until we can just make grpcio an unconditional dependency, that seems like a reasonable tradeoff: it might even help people figure out how to satisfy the optional dependency.

[dhermes]

I am big time 👎 on adding any unnecessary time to running our test suite. Running tests is one of the biggest barriers to contributing.

[tseaver]

On my machine, with this change:

$ time tox -e py27
GLOB sdist-make: /home/tseaver/projects/agendaless/Google/src/gcloud-python/setup.py
py27 inst-nodeps: /home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/dist/gcloud-0.12.0.zip
py27 installed: -f file:///home/tseaver/.pip/wheels,cffi==1.5.2,cryptography==1.3.1,enum34==1.1.2,futures==3.0.5,gcloud==0.12.0,googleapis-common-protos==1.1.0,grpcio==0.13.1,httplib2==0.9.2,idna==2.1,ipaddress==1.0.16,linecache2==1.0.0,nose==1.3.7,nose-exclude==0.4.1,oauth2client==2.0.1,protobuf==3.0.0b2.post2,pyasn1==0.1.9,pyasn1-modules==0.0.8,pycparser==2.14,pyOpenSSL==16.0.0,rsa==3.4.2,six==1.10.0,traceback2==1.4.0,unittest2==1.1.0
py27 runtests: PYTHONHASHSEED='4256048390'
py27 runtests: commands[0] | pip install gcloud[grpc]
Requirement already satisfied (use --upgrade to upgrade): gcloud[grpc] in /home/tseaver/projects/agendaless/Google/src/gcloud-python
----------------------------------------------------------------------
# elided
Ran 1835 tests in 0.864s
OK
___________________________________ summary ____________________________________
py27: commands succeeded
congratulations :)
real 0m8.512s
user 0m7.338s
sys 0m0.975s

With explicit dependencies:

$ time tox -e py27
GLOB sdist-make: /home/tseaver/projects/agendaless/Google/src/gcloud-python/setup.py
py27 inst-nodeps: /home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/dist/gcloud-0.12.0.zip
py27 installed: -f file:///home/tseaver/.pip/wheels,cffi==1.5.2,cryptography==1.3.1,enum34==1.1.2,futures==3.0.5,gcloud==0.12.0,googleapis-common-protos==1.1.0,grpcio==0.13.1,httplib2==0.9.2,idna==2.1,ipaddress==1.0.16,linecache2==1.0.0,nose==1.3.7,nose-exclude==0.4.1,oauth2client==2.0.1,protobuf==3.0.0b2.post2,pyasn1==0.1.9,pyasn1-modules==0.0.8,pycparser==2.14,pyOpenSSL==16.0.0,rsa==3.4.2,six==1.10.0,traceback2==1.4.0,unittest2==1.1.0
py27 runtests: PYTHONHASHSEED='1552785647'# elided
Ran 1835 tests in 0.861s
OK
___________________________________ summary ____________________________________
py27: commands succeeded
congratulations :)
real 0m7.543s
user 0m6.394s
sys 0m0.947s

which is a net cost of one second: hardly worth arguing about.

[dhermes]

I understand the DRY objection but the whole point of using tox is avoiding calling pip install in these cases. The check/install/run flow is not optimized for us manually calling pip install.

[tseaver]

The "wart" (invoking the extra explicitly) will go away once we can safely just depend on grpcio for all supported Python versions. And again, we are talking about one second of wall clock time here per Python 2.7 tox environment: compared to the possibility of having the pinned grcpio version drift between setup.py and tox.ini, that seems like a good tradeoff.

[dhermes]

OK go ahead and merge