Fix base64 flag

[realgam3]

For the people who uses the -b or --print-base64 command argument,
"s_inspector->set_buffer_format(sinsp_evt::PF_NORMAL);" will restore the state to normal dot escaped string instead of base64 (that they chose....).

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What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #987

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Does this PR introduce a user-facing change?:

[poiana]

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[poiana]

Welcome @realgam3! It looks like this is your first PR to falcosecurity/falco 🎉

[leodido]

Hello @realgam3 thanks for submitting this.

Will look deeply into it soon.

In the meantime would you please fill the PR template, provide a good title for the PR, and sign-off your commit?

[leodido]

Hey @realgam3, a friendly ping :)

We need the commits to be signed-off :)

[realgam3]

Hey @realgam3, a friendly ping :)

We need the commits to be signed-off :)
Should I create a new pull request?

[leodido]

Maybe yes! Otherwise I'll use some git magic here as soon I have some spare time :)

[poiana]

LGTM label has been added.

Git tree hash: 55765d89151dac5c7986a05816f654fce68f3dc7

[fntlnz]

@realgam3 sorry CI didn't trigger (we had a problem with some settings earlier)
I'm closing and reopening to let the magic re-happen!

[poiana]

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[fntlnz]

I'm still waiting to merge this because I'm trying to understand how this is related to #581

[fntlnz]

That line was initially removed to support base64 but then was re-added because json was broken https://github.com/falcosecurity/falco/pull/410/files#diff-619b66cc1dd5ce6c64d2aa45a121ad63L127

[fntlnz]

Here's what I get after testing this patch:

Output with this change:

{
  "output": "{\"evt.buffer\":\"IBtbMG0bWzAxOzM0bURlc2t0b3AbWzBtICAgG1swMTszNG1Eb2N1bWVudHMbWzBtICAgG1swMTszNG1Eb3dubG9hZHMbWzBtICAgG1swMTszNG1nbxtbMG0gICAbWzAxOzM0bVBpY3R1cmVzG1swbSAgIBtbMDE7MzRtUHJvamVjdHMbWzBtICAgG1swMTszNG1WaWRlb3MbWzBtICAbWzAxOzM0bSdWaXJ0dWFsQm94IFZNcycbWzBtCg==\",\"evt.time\":1580811468970787674}",
  "priority": "Notice",
  "rule": "Test renzo",
  "time": "2020-02-04T10:17:48.970787674Z",
  "output_fields": {
    "evt.buffer": "IBtbMG0bWzAxOzM0bURlc2t0b3AbWzBtICAgG1swMTszNG1Eb2N1bWVudHMbWzBtICAgG1swMTszNG1Eb3dubG9hZHMbWzBtICAgG1swMTszNG1nbxtbMG0gICAbWzAxOzM0bVBpY3R1cmVzG1swbSAgIBtbMDE7MzRtUHJvamVjdHMbWzBtICAgG1swMTszNG1WaWRlb3MbWzBtICAbWzAxOzM0bSdWaXJ0dWFsQm94IFZNcycbWzBtCg==",
    "evt.time": 1580811468970787600
  }
}

This is wrong because:

• Does base64 formatting but the "output" field becomes a JSON string and contains the content of "output_fields";

Output without this change:

{
  "output": "11:22:08.168296981: Notice Yo (error= .[0m.[01;34mDesktop.[0m   .[01;34mDocuments.[0m   .[01;34mDownloads.[0m   .[01;34mgo.[0m   .[01;34mPictures.[0m   .[01;34mProjects.[0m   .[01;34mVideos.[0m  .[01;34m'VirtualBox VMs'.[0m.)",
  "priority": "Notice",
  "rule": "Test renzo",
  "time": "2020-02-04T10:22:08.168296981Z",
  "output_fields": {
    "evt.buffer": " .[0m.[01;34mDesktop.[0m   .[01;34mDocuments.[0m   .[01;34mDownloads.[0m   .[01;34mgo.[0m   .[01;34mPictures.[0m   .[01;34mProjects.[0m   .[01;34mVideos.[0m  .[01;34m'VirtualBox VMs'.[0m.",
    "evt.time": 1580811728168297000
  }
}

This is wrong because

• No base64

[leodido]

/close in favor of #1033