[PATCH] scripts/ci_build.sh virtualenv uses mktemp to avoid conflicts

Previous user or concurrent users may use scripts/ci_build.sh and in
particular root user creates a temporary directory that is not removable by
common users. Using a combination of mktemp and trap on EXIT will solve
all of these problems.

This patch applies on the top of the current one:

 * scripts/ci_build.sh installs required commands

The patch has been sent by elastic mail and went in moderation as
usual, and here in attachment.

Best regards, R-