autopkgtest fails in bionic

[Balint Reczey]

https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-bionic/bionic/amd64/s/snapcraft/20201213_131445_9471a@/log.gz
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ERROR: test_prime (test_rust_plugin.RustPluginConfinementTestCase)
test_rust_plugin.RustPluginConfinementTestCase.test_prime (classic)
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testtools.testresult.real._StringException: command: {{{/usr/bin/snapcraft}}}
output: {{{
Pulling rust-hello
Downloading 'rustup.sh' 0%
...
Downloading 'rustup.sh' 100%
info: downloading installer
rustup: Unable to run interactively. Run with -y to accept defaults, --help for additional options

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