Enrolling fragments wait cancelled msg then finish itself when user
presses skip button in this page
Bug: 279540275
Test: atest FingerprintEnrollmentActivityTest
Test: For udfps and sfps devices, manually click "Add fingerprint" from
Fingerprint Settings, then quickly back, and quickly re-enter.
Make sure the re-entered enrolling works well.
Change-Id: I99b67af31234f7332ad33e776e82d04ece117e5e