Do not extract ISO with 7z and use mount + rsync instead

Closes-Bug: #1260673

During ISO extraction 7z replaces ':' symbols with '_' and truncates some long file names
for Ubuntu packages which breaks Ubuntu deployment.
Example of broken files after extraction:
bsdutils_1:2.20.1-1ubuntu3_amd64.deb => bsdutils_1_2.20.1-1ubuntu3_amd64.deb
busybox-initramfs_1:1.18.5-1ubuntu4_amd64.deb => busybox-initramfs_1_1.18.5-1ubuntu4_amd64.deb

Change-Id: I4badfcda29c74febb756c6a45b0ed1296cf101a7