Handle invalid shared GIDs.

Shared GIDs are only available inside a range from 50000-59999, so
system UIDs (outside the normal app range) don't have a valid GID to
use.  The best we can do is skip the profile setup in those cases.

Test: builds
Bug: 27948817
Change-Id: I8c38a0e3631eafd07e96da3e37e641b3cce195a6