twister: Don't require test_ prefix to set status

If a test doesn't start with test_, twister currently emits an error:
suite_name.test_name: Unknown status 'started'

Following the suggestion by Maksim Masalski on PR#21191, change the
regex to exclude spaces in the test name, and remove the check that the
test_ prefix exists.

See also #21162

Signed-off-by: Jeremy Bettis <jbettis@google.com>