Change-Id: Ica7d98730bc6f8bd591b44b1e3eec7855d95898a

This reverts commit 73fe802ded9054d2a9e18f83b163565ff425a9b3, reversing
changes made to 13c9ec76aa.

This patch fixes broken dependencies installed via
python-mysqldb which needs mysql-common-5.7.

Signed-off-by: Ondrej Vasko <ondrej.vaskoo@gmail.com>

Mitaka staging test repository for test-kitchen was
missing KEY_ID which prevented apt-get update to
run successfuly.

Signed-off-by: Ondrej Vasko <ondrej.vaskoo@gmail.com>

Galera repository has changed in upstream and has
divided wsrep and galera directories.
This patch sets up 2 repositories `galera-3` and
`mysql`wsrep-5.6`.

Signed-off-by: Ondrej Vasko <ondrej.vaskoo@gmail.com>