Add log collection tool and thread

[pgombar]

Description

This work is the continuation of #1902 and #1847. In this PR there are two main updates:

1. Command-line utility for collecting logs is added.
2. A thread is added that periodically calls the command-line utility to collect logs and upload them to the host. The log collection is invoked with systemd-run and is ran with CPU and memory limits.

Note that the feature is disabled by default for now.

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PR information

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• If applicable, the PR references the bug/issue that it fixes in the description.
• New Unit tests were added for the changes made and Travis.CI is passing.

Quality of Code and Contribution Guidelines

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[kevinclark19a]

FYI, I found the change I made to make ZipFile python2.6 compatible: you can check out this commit in ExperimentalTestFramework's history: 600e6bb41f3d5506543454b27983a04cba1f1930.

Here's the before:

with zipfile.ZipFile(zip_file_buffer, "w", zipfile.ZIP_DEFLATED, False) as file:
    file.writestr("HandlerManifest.json", json.dumps(manifest))
    if extra_files != None:
        for key, value in extra_files.items():
            file.writestr(key, value)

return zip_file_buffer.getvalue()

and here's the after:

file = zipfile.ZipFile(zip_file_buffer, "w", zipfile.ZIP_DEFLATED, False)
try:
    file.writestr("HandlerManifest.json", json.dumps(manifest))
    if extra_files != None:
        for key, value in extra_files.items():
            file.writestr(key, value)

finally:
    file.close()

return zip_file_buffer.getvalue()

Don't know if we want to add python2.6 support in this PR, but this would possibly be useful as a comment to make it easy to add it in a future one.

[pgombar]

Thanks for the analysis! Since we are first targeting VMs with systemd (in order to enable resource limiting), none of them actually run py2.6, so I will take this change when we are expanding to non-systemd VMs. This will be useful for sure!

[larohra]

Initial comments

[larohra]

Some comments on the main code, will review the tests now

[larohra]

Final comments

[larohra]

Thanks for the changes, this would be really helpful once enabled! :)