Reduce container image size with multi-stage builds
Reduce container image size with multi-stage builds

Before this patch, Dockerfile.ubuntu was generating an oversized image.

                       Uncompressed size      Compressed size
Before this patch:     1.3GB                  390MB
After this patch:      250MB                  110MB

tuxology/bcc,tuxology/bcc,brendangregg/bcc,brendangregg/bcc,iovisor/bcc,iovisor/bcc,iovisor/bcc,iovisor/bcc,tuxology/bcc,brendangregg/bcc,brendangregg/bcc,tuxology/bcc,brendangregg/bcc,tuxology/bcc,iovisor/bcc