checkpatch: Disallow glib asserts in main code

Glib commit a6a875068779 (from 2013) made many of the glib assert
macros non-fatal if a flag is set.
This causes two problems:
  a) Compilers moan that your code is unsafe even though you've
     put an assert in before the point of use.
  b) Someone evil could, in a library, call
     g_test_set_nonfatal_assertions() and cause our assertions in
     important places not to fail and potentially allow memory overruns.

Ban most of the glib assertion functions (basically everything except
g_assert and g_assert_not_reached) except in tests/

This makes checkpatch gives an error such as:

  ERROR: Use g_assert or g_assert_not_reached
  #77: FILE: vl.c:4725:
  +    g_assert_cmpstr("Chocolate", >, "Cheese");

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20170427165526.19836-1-dgilbert@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
