replace host_url with application_url

for url http://localhost/infra-optim
pecan.request.host_url is http://localhost
and pecan.request.application_url is http://localhost/infra-optim
we should use application_url to make href in links.

Change-Id: I5d7746b3da196ea2e072fbdf1adb1523ba2bffaf
Closes-Bug: #1854119

watcher/api/controllers/link.py

@@ -23,7 +23,7 @@ from watcher.api.controllers import base
 
 def build_url(resource, resource_args, bookmark=False, base_url=None):
     if base_url is None:
-        base_url = pecan.request.host_url
+        base_url = pecan.request.application_url
 
     template = '%(url)s/%(res)s' if bookmark else '%(url)s/v1/%(res)s'
     # FIXME(lucasagomes): I'm getting a 404 when doing a GET on