Linux CI, Removed cache compression and changed cache key to use image name,...

Linux CI, Removed cache compression and changed cache key to use image name, in order to get more cache hits from jobs sharing the same docker image, modified cache size per key up to 3G to match new needs in cache storage for jobs (ccache will only use 80% of CCACHE_SIZE variable).

Assuming the cache misses are due to the fact that there is a cache id per instance of the runner, that stats display is bugged or that cache hit rate with timestamp for docker is bugged