Make UIDs match in GestureLauncherServiceTest.

Currently, GestureLauncherServiceTest writes settings with
UserHandle.USER_CURRENT and then reads them back with
FAKE_USER_ID = 1337.

This works because FakeSettingsProvider is not multiuser aware.
However, an upcoming CL will make FakeSettingsProvider multiuser aware
so that we can better test multiuser scenarios such as HSUM.

Fix the test so that both reads and writes use
UserHandle.CURRENT. This matches what the service does (it always
reads settings from the current user).

Flag: TEST_ONLY
Test: test-only change
Change-Id: I8729f44a7bed0e758acf85fd7c5bc4740d3597c7