Docker time sync issue while building U20 docker image from U18.

[KiranSukhavasi]

Issue
While building docker images based on Ubuntu 20.04 from a host Ubuntu 18.04 machine, sometimes the build fails because of mismatch in expected system time.

Resolution
We need to disable the time check to build Ubuntu 20.04 based docker images. To do so, use the flag "-o Acquire::Check-Valid-Until=false -o Acquire::Check-Date=false" in the Docker script.

For example,

RUN apt-get -o Acquire::Check-Valid-Until=false -o Acquire::Check-Date=false update -y && apt-get install -y