Fix pipeline for checking Linux agents

[safiuddinr]

For some reason the fleet server is not staying running in the cluster pipeline run. Agents are actually able to get a token and seem to be registering, but the fleet server is not reporting in Elasticsearch GUI.
Find out why it is not running/reporting and make the cluster pipelines begin passing again.

[cbaxley]

The pipeline install is not installing fleet properly in some instances on the cluster pipeline.

[cbaxley]

I have tried modifying post_install in various ways to check for the fleet server and check if elastic is running. So far I haven't resolved it. I am trying a larger virtual machine, which could be the issue.

[cbaxley]

Ok. I have finally updated post install enough to start building consistently. I am going to loop back around and catch a couple of small bugs if I can keep it consistently building.