packages ubuntu: support MySQL 5.7
packages ubuntu: support MySQL 5.7

This fix is used for Xenial.

yoku0825/mroonga,naoa/mroonga,mroonga/mroonga,naoa/mroonga,mroonga/mroonga,yoku0825/mroonga,naoa/mroonga,mroonga/mroonga,yoku0825/mroonga,naoa/mroonga,yoku0825/mroonga,yoku0825/mroonga,naoa/mroonga,naoa/mroonga,yoku0825/mroonga,mroonga/mroonga