Drop requirements-py3.txt

The file was identical to requirements.txt, just reuse this one.

Keep py33 and py34 sections in tox.ini, because eventlet is not tested
yet on Python 3.

Change-Id: I9e49b796692b71bf518e5fbd96b663329cc505b3
Activate pep8 check that _ is imported

Remove the specification in tox.ini that _ is a builtin so that
it will no longer assume that _ does not need to be imported.

This helps ensure that the _ from i18n is used.

Activating this check did not flag any violations.

Change-Id: I34cf8b6358f59583cc178c029ebdd024f583dafe
Port processutils to Python 3

Add encoding and errors parameters to execute() and ssh_execute(). By
default, use the locale encoding in strict mode on Python 2, or the
locale encoding with the 'surrogateescape' error handler on Python 3.

Fix also unit tests to use bytes strings for stdin, stdout and stderr.

Without this change, tests are failing with Python 3 when run with:
PYTHON="python -bb" testr run

Using -bb, Python 3 raises a TypeError when a bytes string is casted
to a text string, which occurred in many places.

Change-Id: I655d5abf932c9a104e3ab487e23c372377f7096a
Merge "Drop requirements-py3.txt"
Merge "Activate pep8 check that _ is imported"