fs_config: generate friendly in AID class

Generate the friendly name in one location. This prepares
the tool for generatting passwd and group files.

Also support mapping friendly names to identifiers.

Test: That output files stay the same as before.
Change-Id: I12198611126613eae81ca61614ed269c2439b72b
Signed-off-by: William Roberts <william.c.roberts@intel.com>