[User Switcher] filter for only full userinfos.

UserInfos are expected to be FLAG_FULL if they are human users. This
will filter out the work profile.

Fixes: 254634782
Test: Add a work profile on device. Observe bouncer user switcher and
dialog user switcher on phone device. Observe that there is no work
profile option.
Test: Added a unit test. Updated the test suite such that human user
infos will be FLAG_FULL

Change-Id: I614dc0c6bf56d888511040ec4db4bfdcf7190f94