Rewrite restorecon python method

[Petr Lautrbach <plautrba@redhat.com>]

Hi.

selinux.restorecon(path, recursive=True) uses matchpathcon() to get a
label for a file and when the label is defined as <<None>>,it throws a
backtrace with error:

"OSError: [Errno 2] No such file or directory"

It creates a problem for scripts which tries to relabel whole directory tree
when there a subdirectory with a specification like this:

/var/lib/nfs/rpc_pipefs(/.*)?      all files   <<None>>

>>> selinux.restorecon('/var/lib', recursive=True)                                   
Traceback (most recent call last):
  File "/usr/lib64/python3.5/site-packages/selinux/__init__.py", line 114, in restorecon
    status, context = matchpathcon(path, mode)
FileNotFoundError: [Errno 2] No such file or directory


At the same time, there's a rfe to rewrite restorecon() to use
selinux_restorecon() which uses selabel_lookup() instead of deprecated
matchpathcon() - [1]

The following 2 patches tries to address the described problem using the RFE.

First patch exports selinux_restorecon() to SWIG bindings.
Second one rewites python implementation of restorecon() to use it.


[1] https://github.com/SELinuxProject/selinux/issues/29

Petr