CI Fixes

* Clean up any previously failed micro deployments before we try to
  deploy. Normally the ensure would take care of this but sometimes
  Jenkins kills our specs so the ensure is not run which leaves the
  system in a weird state.
* Handle the case where our deployments directory is deleted out from
  under us better.
[finishes #48673837] [health_monitor] resurrector should detect when a large number of VMs goes away and not try to recreate the world
[health_monitor] restore error-handling behavior for Alert
[#48673837] [health_monitor] fix ResurrectorHelper specs
Fix health monitor bug with blocking datadog plugin

[Fixes #49800067]
Move net/scp require so scp with gateway will work.
Allow updating an agent on a running stemcell without rebuild.

[Finishes #49035201]
Don't try to tear down the microbosh before deploying in BAT specs
Merge branch 'master' of https://github.com/cloudfoundry/bosh into cloudfoundry-master

Conflicts:
	.gitignore
merge code from cloudfoundry/bosh master