Improve tools/install_docker

[kormat]

• Ensure it is run as root.
• Make it idempotent.
• Support linuxmint as well as plain ubuntu.
• Use non-interactive frontend for apt-get.
• Don't hard-code amd64.

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This change is 

[klausman]

Reviewed 2 of 2 files at r1.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @kormat)

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tools/install_docker, line 8 at r1 (raw file):

# Install prereqs
DEBIAN_FRONTEND=noninteractive apt-get install apt-transport-https ca-certificates curl lsb-release software-properties-common -y

I prefer flags before arguments, so maybe move -y to just after apt-get or install?

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tools/install_docker, line 11 at r1 (raw file):

chksum() {
    echo "$sum $file" | sha256sum --status -c -

This is a bit ugly in that it uses global state instead of parameters.

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tools/install_docker, line 45 at r1 (raw file):

# Install docker-ce
DEBIAN_FRONTEND=noninteractive apt-get install docker-ce=18.06* -y

Same as for line 8 (move -y)

[kormat]

Reviewable status: 1 of 2 files reviewed, 3 unresolved discussions (waiting on @klausman)

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tools/install_docker, line 8 at r1 (raw file):

Previously, klausman (Tobias Klausmann) wrote…

I prefer flags before arguments, so maybe move -y to just after apt-get or install?

Done.

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tools/install_docker, line 11 at r1 (raw file):

Previously, klausman (Tobias Klausmann) wrote…

This is a bit ugly in that it uses global state instead of parameters.

Done.

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tools/install_docker, line 45 at r1 (raw file):

Previously, klausman (Tobias Klausmann) wrote…

Same as for line 8 (move -y)

Done.

[klausman]

Reviewed 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved

[klausman]

Reviewed 1 of 2 files at r3.
Reviewable status: 2 of 3 files reviewed, all discussions resolved (waiting on @klausman)

[klausman]

Reviewed 1 of 2 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved

[klausman]

Reviewed 1 of 1 files at r4.
Reviewable status: complete! all files reviewed, all discussions resolved

[klausman]

Reviewable status: complete! all files reviewed, all discussions resolved

[worxli]

Reviewed 1 of 1 files at r5.
Reviewable status: complete! all files reviewed, all discussions resolved