Execute VCS command in clean environment

Issue #528

Signed-off-by: Michal Čihař <michal@cihar.com>
Clean environment when creating new translation

Issue #528

Signed-off-by: Michal Čihař <michal@cihar.com>
Use subprocess instead of os.system

This allows us better control on environment, we don't have to care
about escaping and avoid extra shell to be executed.

Issue #528

Signed-off-by: Michal Čihař <michal@cihar.com>
Clean environment for ssh key management

Issue #528

Signed-off-by: Michal Čihař <michal@cihar.com>