Add --installroot for yumdownloader to avoid evaluating system packages

When I'm trying build ISO under Fedora I have conflicts like:
Package: python-netaddr-0.7.12-6.2.mira1.x86_64 (proprietary)
    Requires: python(abi) = 2.6
    Installed: python-2.7.5-15.fc20.x86_64 (@updates)
        python(abi) = 2.7
        python(abi) = 2.7
    Installed: python3-3.3.2-18.fc20.x86_64 (@updates)
        python(abi) = 3.3
    Available: python-2.6.6-52.el6.x86_64 (proprietary)
        python(abi) = 2.6
It's because yumdownloader reads host RPMDB.

Change-Id: Ie7a70f3fd6f5098b97e3063c5cb32376a01d6843
Partial-Bug: #1396618
blueprint build-iso-on-fedora
Signed-off-by: Igor Gnatenko <ignatenko@mirantis.com>
Evaluate yum conflicts without duplicates

Enables Fedora to download packages more reliably.

Change-Id: I01ed8ce4863c8ed0fa75e7a6795ec7096ba14793
Partial-Bug: #1396618
blueprint build-iso-on-fedora
Signed-off-by: Igor Gnatenko <ignatenko@mirantis.com>
mirror/ubuntu: use aptly instead of custom scripts

Currently, we are building ubuntu mirror by 'multistrap', then
mkrepo.sh which copying .deb from /var/cache/, downloading
other .deb and .udeb and creating local mirror.

First point is multistrap is not available on RHEL, SUSE, etc.
Second point is building chroot, configuring pkgs, directly
downloading packages is slow and we can't maintenance this bullshit.

Now we will use one docker container, run 'aptly' inside, do mirror all
.udeb and .deb from requirements-deb.txt and pushing it to local_mirror/

blueprint build-iso-on-fedora
Signed-off-by: Igor Gnatenko <ignatenko@mirantis.com>

Change-Id: Ieb23c70f31633f651abc1f8700e039700dca669c