Capture stderr from docker build

BuildKit sends build messages to stderr and python `sh` does nothing
with it. Redirect stderr to our custom printer function to put
everything in the same stream.

Change-Id: Id862154be7ef845a758c5f2248f47a8c6d4de7e2
Signed-off-by: Jonathan Doman <jonathan.doman@intel.com>
1 file changed