Clear identity before calling out to PackageHelper

PackageHelper.resolveInstallLocation expects the binding user to be
equivalent to the calling user. If this is not the case, it may fail
and throw an exception preventing anyone but user 0 from installing
anything.

Bug: 17175251
Change-Id: Id5615738c7b4e1234a548c7b4a410282d14c9ee3
1 file changed