lxc-oracle: fix warnings/errors from some rpm scriptlets

lxc-oracle: fix warnings/errors from some rpm scriptlets

- Some scriptlets expect fstab to exist so create it before doing the
  yum install

- Set the rootfs selinux label same as the hosts or else the PREIN script
  from initscripts will fail when running groupadd utmp, which prevents
  creation of OL4.x containers on hosts > OL6.x.

- Move creation of devices into a separate function

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>