Don't automatically restart jenkins on plugin changes
Don't automatically restart jenkins on plugin changes

This way we can manually gracefully restart jenkins.  Since this
won't immediately install plugins, change the download test to
check whether an hpi or jpi file exists.

Change-Id: I41667684ad8a57f5ae554f866dcc38d5ecca6ba0

open-switch/infra_puppet-jenkins,open-switch/infra_puppet-jenkins