Fix build case + provide repo replace interface

1.Fix the build fails_msg
The commented line is for 'empty_base_image' and another one is based the rhel7 image
2.Provide the repo replace interface
Use two functions to find the Dockerfile's FROM token and replace its value which is what the repo is.
And provide the configuration dockerfile_use_config_repo to control it

Signed-off-by: Time Su <lsu@redhat.com>
I'm a little confused here, if i put docker_repo_name = empty_base_image in the header section [docker_cli/build], and left docker_repo_name = in the sub section, how could i make the case use the repo in default.ini since the sub test ini will override the default one? Need fill it by hand or script ?
What i thought today is keep the option, 'yes' means use the one in default.ini, 'no' then use the one in Dockerfile, ' (empty)' means this case will use url instead of a local file.