Use a stable plugin name.
Use a stable plugin name.

Often the GitHub plugin name has to appear in the Gerrit config
as post-registration or logout URLs.
Making the plugin name fixed and well-known makes this configs more
reliable over time and independent from the different plugin jar
files naming.

Change-Id: I36d04be893065cb1160d39dc1c994f2979d12535

GerritCodeReview/plugins_github,GerritCodeReview/plugins_github,GerritCodeReview/plugins_github