Introduce seapp_neverallow test

Produce a list of neverallow assertions from seapp_contexts into
a separate file, general_seapp_context_neverallows, to be used
during CTS neverallow checking.

Change-Id: I171ed43cf4ae4961f66d5d8f56695345493f1261
Signed-off-by: William Roberts <william.c.roberts@intel.com>