[webrunner] use 1.0 branch in slapos repository

branch 1.0 is pinning the following repositories:
 * erp5
 * vifib
 * wendelin
 * wendelin.core
 * neoppod-repository

For resiliency, it's better to pin the repositories (we want exactly the
same software on runner0 and runner1). If people wants to develop inside
one of those repositories, they will clone it inside srv/runner/project
directory and this will be sync on runner1.

/reviewed-on nexedi/slapos!576

software/slaprunner/instance-runner.cfg

@@ -665,7 +665,7 @@ frontend-domain =
 slapos-repository = https://lab.nexedi.com/nexedi/slapos.git
 slapos-software =
 slapos-software-type =
-slapos-reference = master
+slapos-reference = 1.0
 auto-deploy = false
 auto-deploy-instance = true
 autorun = false