Basic check for homedir permissions

Several guides suggest using data directories under your homedir,
rather than the default /opt area.  This is fine, but on RHEL6 and
similar distros homedirs are very restrictive 0700 permissions which
doesn't allow things like httpd to pass through to serve up files.

Even though stack.sh is taking over the host, changing permissions
automatically is not a nice idea.  So we just warn when it looks like
this is happening.

Change-Id: I9cd70e7fe90638a2a5c3b8fd94756afacac7c7be
Disable selinux for Fedora based distros

selinux locks down httpd which causes various issues for Horizon
working from git checkouts.  Dealing with selinux is more a deployment
than a development issue, so we just disable it for devstack.

Change-Id: I1e61f34e812360dafacd3b3288e66bc9cc5f1648
Fixes: 1175444