Fix checksums and auto-update push

[tomusdrw]

Should go after paritytech/push-release#9 is deployed.

• Common way to compute md5/sha256/sha3 sums
• Safe curl wrapper, which fails the build on non-2xx exit codes.
• Use more specific BUILD_PLATFORM instead of generic PLATFORM when pushing build to updater.

[General-Beck]

it is necessary to check in nightly

[5chdn]

Thanks so much, this was actually on my agenda. Best way to test this is merge and bump nightly, so I agree with @General-Beck here.

[tomusdrw]

Yup, sure. Just wait for the new updater to be deployed.

[5chdn]

Or actually, let me tag this PR once it's deployed. Any ETA?

[tomusdrw]

@5chdn only nightly or ^v\d+.\d+.\d$ tags will now be accepted by the updater. So I think we should do both (or rather all 3):

1. Tag master (should go fine, but should be rejected by the updater)
2. Push to nightly - this should push a new release on kovan.
3. By tagging before the updater is released we can also test a path where the build fails, because updater crashes.

[5chdn]

cc @fevo1971

[5chdn]

This fail is probably related: https://gitlab.parity.io/parity/parity/-/jobs/78627

push release
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed

  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
100   228  100    76  100   152   1374   2748 --:--:-- --:--:-- --:--:--  2763
child "sha3" fails because ["sha3" must only contain hexadecimal characters]\n
Unable to push info to updater service.
ERROR: Job failed: exit code 1

[5chdn]

This probably too: https://gitlab.parity.io/parity/parity/-/jobs/78631

Checksum calculation:
Parity file SHA3: 39746347b20456e15081b540a06188eb41985a1cb56764350a52e53e7ba4db8d
{:timestamp=>"2018-02-12T20:57:29.827336+0000", :message=>"File already exists, refusing to continue: parity-1.10.0-1.x86_64.rpm", :level=>:fatal}
ERROR: Job failed: exit code 1