Investigate reduction of the number of built disk images per target.

Several Yocto builds produce large images in multiple formats.

For example for a typical Minnowboard build 4 almost equally sized results are created:

rw-rr-. 2 go go 1659994112 May 3 15:00 genivi-dev-platform-intel-corei7-64-20170503144726.hddimg
rw-rr-. 2 go go 1651507200 May 3 15:01 genivi-dev-platform-intel-corei7-64-20170503144726.iso
rw-rr-. 2 go go 1617761280 May 3 15:00 genivi-dev-platform-intel-corei7-64-20170503144726.rootfs.ext4
rw-rr-. 2 go go 1598909440 May 3 15:01 genivi-dev-platform-intel-corei7-64-20170503144726.rootfs.wic

Maybe it can't be avoided totally because Yocto is typically set up to create a root file system image no matter what, and only after that can a complete bootable image with partition tables etc. be created. But it's worth looking at what is possible.

Since one can usually be transformed to another it would be better to do such transformatinno in a later dependent pipeline step (when/if desired). Avoiding mulitple large images might speed up the builds and the majority of the builds are intended only to check if compilation was successful.