add mysql minimum version check
add mysql minimum version check

gnocchi indexer can't be used under mysql 5.6.4

Change-Id: Iab008e5f99fa759de8ea6d00d079fc5bc86fadc8
Closes-Bug: #1634374
Co-Authored-By: Hanxi Liu <45d015256b8c69bd7cb5f43d6bc57187477916e4@easystack.cn>

leandroreox/gnocchi,gnocchixyz/gnocchi,sileht/gnocchi,sileht/gnocchi,leandroreox/gnocchi,gnocchixyz/gnocchi