ciao-cli: Validate image file exists when adding a new image.
ciao-cli: Validate image file exists when adding a new image.

Add an image validation in the imageAddCommand function.
If the image/path does not exists it will exit right after, preventing
image creation in the image service.

Fixes https://github.com/01org/ciao/issues/874

Signed-off-by: Erick Cardona <7e10327bafb63098d26367a1914879bbea067098@intel.com>

tpepper/ciao,markdryan/ciao,erick0z/ciao,mrkz/ciao,matthewrsj/ciao,ciao-project/ciao,mcastelino/ciao,mrkz/ciao,obedmr/ciao,mcastelino/ciao,kaccardi/ciao,wcwxyz/ciao,obedmr/ciao,matthewrsj/ciao,mrkz/ciao,kaccardi/ciao,matthewrsj/ciao,rbradford/ciao,wcwxyz/ciao,erick0z/ciao,wcwxyz/ciao,01org/ciao,ciao-project/ciao,markdryan/ciao,erick0z/ciao,rbradford/ciao,mcastelino/ciao,01org/ciao,tpepper/ciao,tpepper/ciao,obedmr/ciao