ipatests: test_sudo: Add coverage for external entries

Covers functionality of external entries for:
* users
* runAsUsers
* groups of RunAsUsers
* runAsGroups
ipatests: test_sudo: Add coverage for category ALL validation

Makes sure sudorules behave correctly both when adding new entries
with corresponding category set to ALL, and when setting the
category to all when corresponding entries exist.

The only exception of deny commands with cmdcategory ALL is
covered as well.
test_sudo: Fix assertions not assuming runasgroupcat set to ALL
ipatests: test_sudo: Do not expect enumeration of runasuser groups