Create newrelic user to fix java and ruby agent installation

[acondrat]

As described in #313, java and ruby agent installation fails because newrelic user does not exist. The user is created when you include newrelic::server_monitor_agent recipe but:
a. you do not want to have server monitor agent installed in some cases
b. it is being deprecated in favor of New Relic Infrastructure. The later does not create a separate user and runs as root.

To solve this, I attempt to create the user unless it already exist.

[acondrat]

Any chance to get this reviewed?

[djoos]

Hi @Condrat,

I'd rather have a check in place that fails if the specified user does not exist. It feels like bloat to add in the user creation in the New Relic cookbook as well...

It's open for discussion though - if the direction is preferred to create the user, then at least the relevant attributes will need to be added on the LWRP, rather than relying on node attributes.

Thanks in advance!
David