Enabling isolated_build breaks package installation

[psafont]

$ tox
.package create: /home/travis/build/common-workflow-language/cwltool/.tox/.package
.package installdeps: setuptools >= 40.0.4, wheel >= 0.29.0
py27-lint create: /home/travis/build/common-workflow-language/cwltool/.tox/py27-lint
py27-lint installdeps: flake8
py27-lint inst: /home/travis/build/common-workflow-language/cwltool/.tox/.tmp/package/1/cwltool-1.0.20181102095220.tar.gz
ERROR: invocation failed (exit code 1), logfile: /home/travis/build/common-workflow-language/cwltool/.tox/py27-lint/log/py27-lint-2.log
ERROR: actionid: py27-lint
msg: installpkg
cmdargs: '/home/travis/build/common-workflow-language/cwltool/.tox/py27-lint/bin/python -m pip install --exists-action w /home/travis/build/common-workflow-language/cwltool/.tox/.tmp/package/1/cwltool-1.0.20181102095220.tar.gz'
Processing ./.tox/.tmp/package/1/cwltool-1.0.20181102095220.tar.gz
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
    IOError: [Errno 2] No such file or directory: '/tmp/pip-req-build-aav9no/setup.py'
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-req-build-aav9no/
py27-lint installed: configparser==3.5.0,cwltool==1.0.20181102095220,enum34==1.1.6,flake8==3.6.0,mccabe==0.6.1,pycodestyle==2.4.0,pyflakes==2.0.0

Example: https://travis-ci.org/common-workflow-language/cwltool/jobs/449757420

Disabling isolated_build works fine: https://travis-ci.org/common-workflow-language/cwltool/jobs/449845321

I'm unsure as to why is it trying to access stup.py in that directory

[gaborbernat]

you've ran into pypa/setuptools#1506

[ryanhiebert]

Thanks, @gaborbernat . I wasn't thinking of any reason why this should have an effect on tox-travis.

[psafont]

Thanks for the quick reply!