Wait for agent startup before updating CAPI tags

[sarah-witt]

What does this PR do?

This PR fixes the conditions when waiting for the agent to start up before running the update script to inject DCA tags. Now the update_agent_config_restart script will not run until either the agent or dogstatsd process is running. This PR also adds more logging.

Description of the Change

Alternate Designs

Possible Drawbacks

Verification Process

Additional Notes

Release Notes

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[keviningvalson]

Since these processes are started using a pid file and it's logically possible for the associated buildpack applications to have a binary with the same name, does use of -F make more sense with pgrep?

[NouemanKHAL]

Yes, it does make more sense. However, when this script is invoked by the Garden API, the underlying process doesn't have the DATADOG_DIR ENV variable, which we would need to find the pid file (e.g.: ${DATADOG_DIR}/run/agent.pid) . @sarah-witt was using this approach as a temporary workaround. We didn't want to assume that DATADOG_DIR=/home/vcap/app/.datadog without careful consideration, as we noticed in some parts in the scripts DATADOG_DIR could be a user input.
We're going to make a separate PR to address this issue and then we'll resume this PR.