Retry on error

[iainelder]

Retry each installer test once after an error.

If it's an intermittent error caused by a flaky network, then the second attempt may just work.

If it fails twice, it's more likely to require a change and so needs my attention.

Today the Test all installers run 21 failed because of an apparently flaky download server. See #6 for details.

[iainelder]

Details from #6:

This time it seems to be a problem from the GNU parallel download server.

Ubuntu 20:

+ browser_download_url=https://ftpmirror.gnu.org/parallel/parallel-latest.tar.bz2
++ curl --silent --show-error --url https://ftpmirror.gnu.org/parallel/parallel-latest.tar.bz2 --location --remote-name --write-out '%{filename_effective}'
++ command curl --netrc --silent --show-error --url https://ftpmirror.gnu.org/parallel/parallel-latest.tar.bz2 --location --remote-name --write-out '%{filename_effective}'
++ curl --netrc --silent --show-error --url https://ftpmirror.gnu.org/parallel/parallel-latest.tar.bz2 --location --remote-name --write-out '%{filename_effective}'
curl: (7) Failed to connect to ftpmirror.gnu.org port 443: Connection timed out
+ download_filename=parallel-latest.tar.bz2

Ubuntu 22:

+ browser_download_url=https://ftpmirror.gnu.org/parallel/parallel-latest.tar.bz2
++ curl --silent --show-error --url https://ftpmirror.gnu.org/parallel/parallel-latest.tar.bz2 --location --remote-name --write-out '%{filename_effective}'
++ command curl --netrc --silent --show-error --url https://ftpmirror.gnu.org/parallel/parallel-latest.tar.bz2 --location --remote-name --write-out '%{filename_effective}'
curl: (28) Failed to connect to ftpmirror.gnu.org port 443 after 134601 ms: Connection timed out
+ download_filename=parallel-latest.tar.bz2