[iec] Add basic CentOS support (virtual only)

[iec] Add basic CentOS support (virtual only)

- reclass: iec: CentOS compatibility changes:
  * drop `proto: static` in favor of letting the linux formula set
    the appropiate default based on target OS;
  * replace `proto: manual` with `proto: none` on RHEL systems;
  * system.file: Avoid using non-existing `shadow` group for system
    files;
  * load br_netfilter kernel module to avoid `linux.network` state
    failures;
  * disable `at`, `cron` due to incomplete defaults in
    salt-formula-linux (since we don't use them on iec nodes anyway);
- jumpserver/VCP VMs: centos: enable predictable interface names:
  * CentOS cloud image defaults to old 'eth' naming scheme;
  * add necessary kernel boot options via linux state;
  * cleanup auto-generated udev rules for old eth interface names;
- salt-formula-linux: network: RHEL: Set bridge for member interfaces
  * Find the bridge containing the interface being currently
    configured (if any) and pass it to the `network.managed` Salt call;
- deploy.sh: Add new deploy argument `-o` for specifying the operating
  system to preinstall on jumpserver and/or VCP VMs;
  * defaults to 'ubuntu1604';
  * only iec scenarios will also support 'centos' for now;
- user-data: minor tweaks for CentOS compatability:
  * use `systemctl` instead of `service` utility;
  * explicitly enable `salt-minion` service, since it defaults to
    disabled on RHEL systems;
  * explicitly call `ldconfig` to work around stale cache on RHEL,
    preventing `salt-minion` from using OpenSSL library;
- states: virtual_init: Skip non-existing sysctl options on CentOS:
  * CentOS currently uses a 3.x kernel which lacks certain sysctl
    options that were only introduced in 4.x kernels, so skip them;
- state: akraino_iec: Add centos support:
  * move iec repo to `/var/lib/akraino/iec` on both Salt Master and
    cluster nodes;
- scenario defaults: Add CentOS configuration:
  * OS-dependent configuration split;
  * CentOS base image, default packages etc.;
- AArch64 deploy requirements: Add `xz` dependency
  * CentOS AArch64 cloud image is archived using xz, install xz tools
    for decompression;
- xdf_data: Make yaml parsing OS agnostic:
  * rename `apt` to `repo` where appropiate;
  * OS-dependent configuration parsing;
- lib_jump_deploy: CentOS handling changes:
  * skip filesystem resize of cloud image for CentOS;
  * add repo handling, package intallation/removal handling for CentOS;
  * unxz base image if necessary (CentOS AArch64 cloud image);

Change-Id: Ic3538bacd53198701ff4ef77db62218eabc662e7
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>