Add the coverity badge back
Add the coverity badge back

Coverity was down for a few weeks and we assumed the free service was
gone so we removed the badge. But it came back again so the badge is
back.

HiOA-ABI/nikita-noark5-core,HiOA-ABI/nikita-noark5-core,HiOA-ABI/nikita-noark5-core,HiOA-ABI/nikita-noark5-core