ci_cmake: Add flag to skip container execution

`--skip-container` inline argument is introduced to skip
container execution when it is set.
This could be useful for developers who run locally the script
but wish to skip the container spawning to speed-up developing
and testing.

Signed-off-by: Leandro Belli <leandro.belli@arm.com>
Change-Id: Ib44aea5953d6017a4bac4ac6dd5fd9fe91c21d2a