afb-api-so: Exclude directories starting with .

afb-api-so: Exclude directories starting with .

Exclude from the search of bindings any
directory starting with a dot (.) by default.

It is possible to reactivate the prvious behaviour
by defining the following preprocessor variables

 - AFB_API_SO_ACCEPT_DOT_PREFIXED_DIRS

   When this variable is defined, the directories
   starting with a dot are searched except
   if their name is "." or ".." or ".debug"

 - AFB_API_SO_ACCEPT_DOT_DEBUG_DIRS

   When this variable is defined and the variable
   AFB_API_SO_ACCEPT_DOT_PREFIXED_DIRS is also defined
   scans any directory not being "." or "..".

The previous behaviour was like difining the 2 variables,
meaning that only . and .. were excluded from the search.

This change is intended to definitely solve the issue
SPEC-662. Yocto installed the debugging symbols in the
subdirectory .debug. For example the binding.so also
had a .debug/binding.so file attached. Opening that
debug file made dlopen crashing.
See https://sourceware.org/bugzilla/show_bug.cgi?id=22101

Bug-AGL: SPEC-662

Change-Id: Ic38a83aaa5f16d938e504aba66597bb9a219c193
Signed-off-by: José Bollo <jose.bollo@iot.bzh>