explicitly handle SIGINT and SIGTERM

[joelanford]

Description of the change:

This PR adds explicit handling for SIGINT and SIGTERM, so that we can catch those signals and propagate them via a Go context to long running processes in order to perform a graceful shutdown.

Motivation for the change:

Temporary files are being left behind because defer statements are not executed when these signals are not caught and handled by the program. This PR ensures that we run defer statements prior to exiting.

Reviewer Checklist

• Implementation matches the proposed design, or proposal is updated to match implementation
• Sufficient unit test coverage
• Sufficient end-to-end test coverage
• Docs updated or added to /docs
• Commit messages sensible and descriptive

[openshift-ci]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.53%. Comparing base (1f9e725) to head (6a917e9).
Report is 15 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1448      +/-   ##
==========================================
+ Coverage   48.47%   48.53%   +0.05%     
==========================================
  Files         136      135       -1     
  Lines       12814    12800      -14     
==========================================
  Hits         6212     6212              
+ Misses       5561     5547      -14     
  Partials     1041     1041              

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[perdasilva]

If I understand the changes correctly, we are now using the signal package to create a top context that will cancel on SIGINT or SIGTERM. This context is set as the cmd context, and each (long running) opm command creates a sub-context (with the top level context as parent) for its work. These commands also spawn a go routine to monitor the context and shutdown gracefully if it gets cancelled. Therefore, if the command's context gets cancelled -> graceful shutdown, if the process gets a SIGINT or SIGTERM, the top level process gets cancelled and propagates down to the sub-contexts -> graceful shutdown.

We're getting a breaking api change by deleting shutdown.go - but that should be ok as this package is only really meaningful for the command structure (as opposed to manipulating catalog content). So, lgtm ^^

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: joelanford, perdasilva

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[grokspawn]

/lgtm