Add support for Oracle Linux 7 and CentOS 7

Add support for Oracle Linux 7.0 (RHCK - Red Hat Compatible Kernel **ONLY** for now) and CentOS 7.

Difference between Oracle Linux 7.0 and CentOS 7.0

CentOS 7.0
* For some reason `yum-builddep kernel` is missing `audit-libs-devel` which will cause `rpmbuild  --target=x86_64 /root/rpmbuild/SPECS/kernel.spec` to fail. However, Oracle Linux 7.0 does count it. So added it in `kpatch-build` dependencies.
* `debug` repo needs to be enabled for `yum-builddep kernel` and `debuginfo-install kernel` to work.

Oracle Linux 7.0
* So far [debuginfo](https://oss.oracle.com/ol7/debuginfo/) has been made a repo yet (no repodata directory), it cannot be added as a repo. So kernel debuginfo packages have to be manually installed as workaround. Will update this later when it is made a repo (the Oracle dudes need to run `createrepo` on their end).
* `ol7_optional_latest` repo needs to be enabled (by default disabled) for `yum-builddep kernel` and `debuginfo-install kernel` to work.

Tested and confirmed to work on Oracle Linux 7.0 x86_64 [screenshot](https://flic.kr/p/ov7aBa) and CentOS 7.0 x86_64 [screen](https://flic.kr/p/oLxuY5).

Looks like Oracle Linux 7 is more in line with upstream RHEL 7 ;-D