Add Python 3 support

[OndrejSlamecka]

Makes setroubleshootd and sealert work with Python 3.

We'll want to merge this with https://github.com/OndrejSlamecka/setroubleshoot/tree/feature-python3non_packaged_tools

Specfiles for Fedora packages:

• setroubleshoot http://paste.fedoraproject.org/255070/54561214
• setroubleshoot-plugins http://paste.fedoraproject.org/253742/92778461

[bachradsusi]

make dist fails:

make[2]: Entering directory '/home/bachradsusi/devel/src/github/fedora-selinux/setroubleshoot.git/framework/gui'
make[2]: *** No rule to make target 'bug_report.glade', needed by 'distdir'.  Stop.
make[2]: Leaving directory '/home/bachradsusi/devel/src/github/fedora-selinux/setroubleshoot.git/framework/gui'
Makefile:823: recipe for target 'distdir' failed
make[1]: *** [distdir] Error 1
make[1]: Leaving directory '/home/bachradsusi/devel/src/github/fedora-selinux/setroubleshoot.git/framework'
Makefile:922: recipe for target 'dist' failed
make: *** [dist] Error 2

[bachradsusi]

This pull request is already merged in python3 branch. Thanks!