Rename avocado.core.error_codes to avocado.core.exit_codes.

Signed-off-by: Rudá Moura <rmoura@redhat.com>
avocado.core.exit_codes: Use constant exit codes.

Create constants which maps the exit codes.
Remove the previous dictionary with exit codes (numeric_status).

Signed-off-by: Rudá Moura <rmoura@redhat.com>
avocado.job: Use constants from avocado.core.exit_codes.

Using exit constants from avocado.core.exit_codes.

Signed-off-by: Rudá Moura <rmoura@redhat.com>
avocado.plugins: Use constants from avocado.core.exit_codes.

Using exit constants from avocado.core.exit_codes.

Signed-off-by: Rudá Moura <rmoura@redhat.com>
Merge pull request #312 from ruda/rename_to_exit_codes

Use module avocado.core.exit_codes [V1]