CtsFsMgrTestCases secondary_user

Marks this CTS test module as supporting secondary_user, meaning that
the tests are eligible to be run from a regular Android user other
than the system user (i.e. other than user 0).

Note that 'user' here refers to the concept of users in Android
Multiuser; it is NOT the same as a uid.

Bug: 141773058
Test: module passed with secondary_user params
 (--enable-optional-parameterization --module-parameter secondary_user)

Change-Id: I1829a4297a49cd38b4b8a2558c92941acab8ab9a