libsepol/cil: Add userattribute{set} functionality

This adds a userattribute statement that may be used in userroles and
constraints. The syntax is the same as typeattributset.

Also, disallow roleattributes where roles are accepted in contexts.

Specify a userattribute

    (userattribute foo)

Add users to the set foo

    (userattributeset foo (u1 u2))

Signed-off-by: Yuli Khodorkovskiy <ykhodorkovskiy@tresys.com>
Signed-off-by: James Carter <jwcart2@tycho.nsa.gov>
19 files changed