[CI] Improve error catching and build log verbosity

Summary:
Avoid missing errors from pipes and make the script print itself as it
runs. This will make the build logs more verbose and easier to debug
should an issue occur.

Test Plan: Run the CI build and gitian build, and check there is no error.

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D3992