Change event text based on assertion/deassertion
Change event text based on assertion/deassertion

For the text description and severity, use the negated values
added previously to make it more clear what an event represents.

Change-Id: I9eb47363d5f190bd0fd5bec58bc49fa12a9a3ed0

openstack/pyghmi,openstack/pyghmi,stackforge/pyghmi,benoit-canet/pyghmi