fix N402 for nova/db

fixes N402 (single line docstring must end in a period) for nova/db

Change-Id: I31779cbf83fa77c7cc382cce1667812f8cdecd61
fix N402 for nova/c*

fix N402 (single line docstring comments should end in a period)
for nova/cells, nova/compute, and nova/conductor

Change-Id: Ia2d4e64f4dde346a26aeba8cf10dd2000585caa0
Merge "fix N402 for nova/db"
Merge "fix N402 for nova/c*"