Fix: local calls to pre-commit tox profile

Fix: local calls to pre-commit tox profile

When run locally, pre-commit tox profile resulted in the following
failure:
$ tox -e pre-commit
[..]
gitlint...........................................................Failed
- hook id: gitlint
- exit code: 254

An error occurred while executing \
'/usr/bin/git config --get user.name': b''

The reason behind is that tox virtualenv cannot directly access the
$HOME shell variable to retrieve the local git configuration unless
this variable is explicitly declared accessible via the passenv tox
parameter.
This is required by gitlint to retrieve the correct git configuration
parameters.

Signed-off-by: Guillaume Lambert <guillaume.lambert@orange.com>
Change-Id: I99197f88cf4024a5922fe62ec07610921dcf515f