internal/build: show ppa upload process stdout on stdout

[holiman]

The travis sftp upload to ppa dies after 10m of inactivity. Hard to say what happens (we do get a notification about a successful upload from ppa), but directing the process stdout to stdout seems like thing that might tell us more.

[holiman]

Closer, but not good enough.

Before

put /tmp/geth-build-1023977950/ethereum-unstable_1.10.17+build27737+trusty_source.changes ~ethereum/ubuntu/ethereum/ethereum-unstable_1.10.17+build27737+trusty_source.changes
put /tmp/geth-build-1023977950/ethereum-unstable_1.10.17+build27737+trusty_source.buildinfo ~ethereum/ubuntu/ethereum/ethereum-unstable_1.10.17+build27737+trusty_source.buildinfo
Warning: Permanently added the RSA host key for IP address '91.189.95.85' to the list of known hosts.
Connected to ppa.launchpad.net.
No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#build-times-out-because-no-output-was-received

After

put /tmp/geth-build-1040236554/ethereum-unstable_1.10.17+build27738+trusty_source.changes ~ethereum/ubuntu/ethereum/ethereum-unstable_1.10.17+build27738+trusty_source.changes
put /tmp/geth-build-1040236554/ethereum-unstable_1.10.17+build27738+trusty_source.buildinfo ~ethereum/ubuntu/ethereum/ethereum-unstable_1.10.17+build27738+trusty_source.buildinfo
Warning: Permanently added the RSA host key for IP address '91.189.95.85' to the list of known hosts.
Connected to ppa.launchpad.net.
sftp> put /tmp/geth-build-1040236554/ethereum-unstable_1.10.17+build27738+trusty.tar.xz ~ethereum/ubuntu/ethereum/ethereum-unstable_1.10.17+build27738+trusty.tar.xz
Uploading /tmp/geth-build-1040236554/ethereum-unstable_1.10.17+build27738+trusty.tar.xz to ./~ethereum/ubuntu/ethereum/ethereum-unstable_1.10.17+build27738+trusty.tar.xz
sftp> put /tmp/geth-build-1040236554/ethereum-unstable_1.10.17+build27738+trusty.dsc ~ethereum/ubuntu/ethereum/ethereum-unstable_1.10.17+build27738+trusty.dsc
Uploading /tmp/geth-build-1040236554/ethereum-unstable_1.10.17+build27738+trusty.dsc to ./~ethereum/ubuntu/ethereum/ethereum-unstable_1.10.17+build27738+trusty.dsc
sftp> put /tmp/geth-build-1040236554/ethereum-unstable_1.10.17+build27738+trusty_source.changes ~ethereum/ubuntu/ethereum/ethereum-unstable_1.10.17+build27738+trusty_source.changes
Uploading /tmp/geth-build-1040236554/ethereum-unstable_1.10.17+build27738+trusty_source.changes to ./~ethereum/ubuntu/ethereum/ethereum-unstable_1.10.17+build27738+trusty_source.changes
sftp> put /tmp/geth-build-1040236554/ethereum-unstable_1.10.17+build27738+trusty_source.buildinfo ~ethereum/ubuntu/ethereum/ethereum-unstable_1.10.17+build27738+trusty_source.buildinfo
Uploading /tmp/geth-build-1040236554/ethereum-unstable_1.10.17+build27738+trusty_source.buildinfo to ./~ethereum/ubuntu/ethereum/ethereum-unstable_1.10.17+build27738+trusty_source.buildinfo
No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#build-times-out-because-no-output-was-received