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>