(PUP-3151) Added acceptance test for External CA on Jetty

This commit adds an acceptance test which exercises External CA
functionality against a Jetty configuration.
(PUP-3151) Removed newline from host_entry test fixture

This commit removes the newline character from the end of the host_entry
method in the acceptance test ExternalCertFixtures.  The presence of this
character was causing the jetty_external_root_ca.rb test, when run on
Debian, to not properly set the needed hostname entry into the
/etc/hosts file.
Merge pull request #3028 from camlow325/maint/master/PUP-3151-jetty-external-root-ca-test

(PUP-3151) Added acceptance test for External CA on Jetty