Enhance repo creation scripts idempotency by supporting caching

Enhance repo creation scripts idempotency by supporting caching

While 'yumdownloader' and 'apt-get download' commands do not
re-download packages that are already present in working dir,
scripts still need to perform package dependencies resolution
which is a time consuming activity hence a feature was added to
skip any further actions (download or deps resolution) on packages
that are already present locally.

For cold versus warm cache the gain in run time is:

       cold     warm
RPM     90s      10s
DEB     7m       90s

Change-Id: Ie502934cff6484844557832251e7ce0991789cfb
Issue-ID: OOM-2635
Signed-off-by: Bartek Grzybowski <b.grzybowski@partner.samsung.com>