lxc-oracle: allow installing from arbitrary yum repo

With this change, you can install a container from a mounted .iso, or any
yum repo with the necessary packages. Unlike the --url option, the repo
does not need to be a mirror of public-yum, but the arch and release must
be specified. For example to install OL6.5 from an .iso image:

mount -o loop OracleLinux-R6-U5-Server-x86_64-dvd.iso /mnt
lxc-create -n OL6.5 -t oracle -- --baseurl=file:///mnt -a x86_64 -R 6.5

The template will create two yum .repo files within the container such that
additional packages can be installed from local media, or the container can
be updated from public-yum, whichever is available. Local media must be bind
mounted from the host onto the containers' /mnt for the former .repo to work:

mount --bind /mnt $LXCPATH/OL6.5/rootfs/mnt

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
lxc-oracle: update to support OL7

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