Drop requirement on octavia-lib

octavia-lib is only required to get a constant which actually should be
in the octavia-tempest-plugin codebase like other protocols are.

Change-Id: I269da85a9a7adabce340aa436d9457b12dee6e36
diff --git a/octavia_tempest_plugin/common/constants.py b/octavia_tempest_plugin/common/constants.py
index 0122424..5503b7f 100644
--- a/octavia_tempest_plugin/common/constants.py
+++ b/octavia_tempest_plugin/common/constants.py
@@ -101,6 +101,7 @@
 HTTP = 'HTTP'
 HTTPS = 'HTTPS'
 TCP = 'TCP'
+TERMINATED_HTTPS = 'TERMINATED_HTTPS'
 
 # HTTP Methods
 GET = 'GET'