Rename default to 'browsertest'

The 'global' default is applied on any change. In preparation for a
merge of the cloudbees branch to the master branch, rename the
browsertests specific defaults to 'browsertests' and apply them to the
job templates with:

 defaults: browsertests

No jobs changed.

Change-Id: I3a684ff1c4e7de2148151843d9e73f5bb7d7c574
Rename build 'default' to 'browsertest-website'

That makes more sense. Also moved that builder macro to macro.yaml.

Change-Id: I6d2b708cdcd42c0aa90c039a2839beb0ac939d5d