Some improvements to tox-bootstrapd's Dockerfile

[nurupo]

Users probably shouldn't run toxcore master, running the highest version tag sounds better.

Switched it to use cmake to build toxcore instead of sing autotools while I was at it, since we are supposedly phasing out autotools at some point (maybe?).

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This change is 

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[iphydf]

Reviewed 4 of 4 files at r1.
Reviewable status: 0 of 1 approvals obtained

[nurupo]

Rebased and CI passes. Removing the CI enabling commit.

[iphydf]

LGTM - feel free to rebase and merge (I can't do it for you).

[codecov]

Codecov Report

Merging #1211 into master will decrease coverage by <.1%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #1211     +/-   ##
========================================
- Coverage      83%   82.9%   -0.1%     
========================================
  Files          82      82             
  Lines       14692   14645     -47     
========================================
- Hits        12195   12143     -52     
- Misses       2497    2502      +5

Impacted Files	Coverage Δ
toxcore/TCP_server.c	75.9% <0%> (-4.4%)	⬇️
toxcore/Messenger.c	86.5% <0%> (-0.6%)	⬇️
toxcore/DHT.c	76.6% <0%> (-0.2%)	⬇️
toxcore/onion_client.c	95.9% <0%> (-0.1%)	⬇️
toxav/toxav.c	67.3% <0%> (ø)	⬆️
toxcore/net_crypto.c	94.8% <0%> (ø)	⬆️
toxav/msi.c	64.2% <0%> (+0.2%)	⬆️
toxcore/group.c	76.4% <0%> (+0.3%)	⬆️
auto_tests/save_load_test.c	98.6% <0%> (+0.5%)	⬆️
toxcore/friend_connection.c	94.5% <0%> (+1.4%)	⬆️
... and 2 more

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[nurupo]

Done.

Thanks for removing the WIP.

Have you noticed that while Dockerfile checks out the greatest version number tag, the CI script seds the Dockerfile to run tests against the current changes instead? You should have seen that if you checked the patch, though I decided to point it out. I was looking for some Dockerfile condition thingy where it would do different thing if CI=true env variable is set, but alas there is no such functionality, at least not in the building stage of the container.

[iphydf]

Yes, I noticed that when I was adding a test for the alpine dockerfile (which I then deleted - and I dropped the PR for testing the dockerfile). LGTM => rebase.

[nurupo]

Rebased.