Currently if container registry is inaccessible the image will be built
locally and that takes time. This patch adds support to use mirror
registry. To use a different registry CTR_IMAGE environment variable
must be set. For example:
CTR_IMAGE="registry/cloud-hypervisor" scripts/dev_cli.sh
or
export CTR_IMAGE="registry/cloud-hypervisor"
scripts/dev_cli.sh
Signed-off-by: Ruslan Mstoi <ruslan.mstoi@intel.com>