python/chcat: fix removing categories on users with Fedora default setup

Using Vagrant with fedora/28-cloud-base image, SELinux logins are
configured this way:

    # semanage login -l
    Login Name           SELinux User         MLS/MCS Range        Service

    __default__          unconfined_u         s0-s0:c0.c1023       *
    root                 unconfined_u         s0-s0:c0.c1023       *
    vagrant              unconfined_u         s0-s0:c0.c1023       *

Using "chcat -l +c42 vagrant" successfully adds the category to user
vagrant, but "chcat -l -- -c42 vagrant" fails to remove it.
semanage login -l returns:

    vagrant              unconfined_u         s0-s0:c0.c1023,c42   *

This issue is caused by expandCats(), which refuses to return a list of
more than 25 categories. This causes chcat_user_remove() to work with
cats=['c0.c1023,c42'] instead of cats=['c0.c102','c42'], which leads to
it not been able to remove 'c42' from the list.

Fix this issue by splitting the list of categories before calling
expandCats().

Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
diff --git a/python/chcat/chcat b/python/chcat/chcat
index 73f7572..5bef007 100755
--- a/python/chcat/chcat
+++ b/python/chcat/chcat
@@ -82,8 +82,7 @@
         if len(serange) > 1:
             top = serange[1].split(":")
             if len(top) > 1:
-                cats.append(top[1])
-                cats = expandCats(cats)
+                cats = expandCats(top[1].split(','))
 
         for i in newcat[1:]:
             if i not in cats:
@@ -163,8 +162,7 @@
         if len(serange) > 1:
             top = serange[1].split(":")
             if len(top) > 1:
-                cats.append(top[1])
-                cats = expandCats(cats)
+                cats = expandCats(top[1].split(','))
 
         for i in newcat[1:]:
             if i in cats: