Add site.settings to buildbot scons configuration.

Adding site.setting to buildbot configuration to move buildslave PATH
variable into scons environment path. This supports use of custom gcc
build in hyak.
Adding buildslave utility scripts need for hyak buildslave.

Adding buildslave_blocking_start script, for use in queue buildslave
runs via pbs. Adding start_hyak_buildslave script, which queues a
buildslave tasks and opens tunneled ports via ssh.
Add ssh batch mode to start_hyak_buildslave.
Adding initial digs deployment scripts.
Add basic change hooks and release branch poll & submit script.
Add environment build properties to automated release builds.
Fix start_hyak_buildslave logging and ssh key validation.
Add option to symlink deployed build results.

Adding option --link_current to deploy_build.py and equivalent
deploy_current_build buildbot property. Option triggers creation of
'current' symlinks in deployed build directory linking to the deployed
build product. Adding option in buildbot force build page to trigger
symlink creation.
Adding default parameters to buildbot force schedulers.
Update buildbot to target packged_bindings binding directory.
Mandate username in force scheduler.