test_server improvements

When running in UNIT_TEST mode, only run the tests of the tested addon, not of
its dependencies. This saves time as the tests of the dependencies are not run
again and again for each addon being tested. We keep the current behavior in
non UNIT_TEST mode to let Odoo sort out the modules dependencies (this is
important for a repository containing e.g. both sale and sale_stock: if both
addons are installed first, and then tested, the tests of sale will fail. The
case does not happen in UNIT_TEST model)

Use the list syntax of subprocess rather than interpolated strings

Use subprocess.Popen rather than a subshell to handle the pipe.
reduce verbosity of the non test odoo runs

set these to log-level warning instead of info. The goal is to
reduce the verbosity of the output in the travis logs, esp. for
things which should be green.
remove early fail in UNIT_TEST mode

We keep testing even if one of the addons failed.

Display a summary of success / failures
fix log-level
fix: don't use relative imports in a script
fix false positive in check loaded

only check loaded modules when the log level ensures that we have this
information.
cleanup unused variables
fix log level config

use log level 'test' in odoo << 8.0 and 'info' in >= 8.0
Merge pull request #129 from gurneyalex/improve_test_server

Improve test server
[ADD] odoolint: Adding pylint plugin of odoolint.
[REF] pylint: Enable pylint plugin: odoolint