Ignore GrantCredentials call with unexpected calling uid.

Activity can be used only in two cases.
1) Calling uid matches uid grantee.
2) Calling uid is is system. This flow is used by getToken methods with

Test: Existing CTS tests
Bug: 158480899
Change-Id: I1421c333b6cebb4f7cddcdd8766298f6872e933b
(cherry picked from commit 10d8a114bbd91c07f2feb5009328b16203ff50b1)
1 file changed