Fix: bandit pre-commit hook exclude regex

Fix: bandit pre-commit hook exclude regex

The 'exclude' field in pre-commit hook is a regex, not a glob,
as it is advertised by pre-commit runtime warnings.
"tests/*" matches "tests", "tests/" or "tests//...///" but also any file
or folder, not necessarily at the root of the project, that contains
"tests" in its name.
The right regex to ignore the tests folder at project root is "^test/"

Signed-off-by: Guillaume Lambert <guillaume.lambert@orange.com>
Change-Id: I74e22bff98c78a7d0dbabac81fdda7b07ed50d4f