Fix only partial rollback of Smack rules

Fix only partial rollback of Smack rules

Some tests temporarily add new Smack rules in order to test unprivileged
access to system services. After the test, they are cleared with
smack_revoke_subject. However, this only removes rules where the test
application is the subject.

I have replaced calls where this is an issue with a smack_accesses_clear
call, which removes all rules loaded with a given handle. Since affected
tests do not modify Smack rules in any other way and only use test
labels for fake apps, no rules removed by the old call and not by the
new call can exist.

Change-Id: I841d6b7ad05549d8837645e3d9176f4db7029908