Trust the “system user” for purposes of whole-script approval when Jenkins is unsecured.
In this case, there is no attempt at security, so there is no point in considering who has configured a script.
This change also reduces the amount of work needed to make JenkinsRule tests pass
after adding script-security integration to a plugin: most tests do not configure security, so preapproveAll is not needed.
[maven-release-plugin] prepare release script-security-1.4