Raise build_timeout from 60 to 300

A lot of build timeout was seen, for example:
http://logs.openstack.org/17/606417/1/check \
/octavia-v2-dsvm-scenario-centos-7/0b4c23a/testr_results.html.gz

Try to raise the default and see if it helps.

Change-Id: Id6dfd80f04624e845807f2a20f2f4e816a778415

octavia_tempest_plugin/config.py

@@ -51,7 +51,7 @@ OctaviaGroup = [
                help='Time in seconds between build status checks for '
                     'non-load-balancer resources to build'),
     cfg.IntOpt('build_timeout',
-               default=60,
+               default=300,
                help='Timeout in seconds to wait for non-load-balancer '
                     'resources to build'),
     # load-balancer specific options