bitbake: parse: Return IOError when including file with absolute path

bitbake: parse: Return IOError when including file with absolute path

* resolve_file was behaving different when relative and absolute
  paths were passed to it

* include relative-path/non-existent-file.inc
  works correctly resolve_file throws IOError, BBHandler.py:handle()
  doesn't catch it, ConfHandler.py:include() catches IOError and shows:
  DEBUG: CONF file 'relative-path/non-existent-file.inc' not found
* include /absolute-path/non-existent-file.inc
  was failing, because resolve_file just returns fn,
  BBHandler.py:handle() calls bb.parse.mark_dependency(d, abs_fn)
  which throws:
  OSError: [Errno 2] No such file or directory: '/absolute-path/non-existent-file.inc'
  and parsing fails.
  Ad isfile() test for absolute fn and throw IOError to make
  resolve_file behavior consistent for both paths.

* I know we had some issues with -b relative-path-to-recipe.bb and
  absolute path, so consider this patch only as RFC and documentation of
  this problem

* Catch OSError too in ConfHandler.py:include() e.g. in case the file exists, but user
  cannot read it or something like that.

(Bitbake rev: b0bbd89a4f0b98fa1ab28b8e0526cd9ddb76fa57)

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>