Install test_server.bin in well known location

This patch installs and uses test_server.bin from
/opt/octavia-tempest-plugin as a well known location on the
filesystem. This way tests, like grenade, that run the devstack
plugins once in /old paths, can find the binary when running from
/new paths.

Change-Id: Ia78f16fde026269dec01f4dceb202842ad12a557
diff --git a/octavia_tempest_plugin/config.py b/octavia_tempest_plugin/config.py
index 77d2f6e..f44bf96 100644
--- a/octavia_tempest_plugin/config.py
+++ b/octavia_tempest_plugin/config.py
@@ -213,6 +213,10 @@
                default='/var/log/octavia-amphora.log',
                help='File path, on the tempest system, to the amphora admin '
                     'log file.'),
+    cfg.StrOpt('test_server_path',
+               default='/opt/octavia-tempest-plugin/test_server.bin',
+               help='Filesystem path to the test web server that will be '
+                    'installed in the web server VMs.'),
 ]
 
 lb_feature_enabled_group = cfg.OptGroup(name='loadbalancer-feature-enabled',