jjb: lttng-tools: Unify rootbuild jobs under '_root_{buildtype}'

jjb: lttng-tools: Unify rootbuild jobs under '_root_{buildtype}'

Replace the old '_rootbuild' jobs with the same template as used by
the el8/sles15sp4 root jobs. Replace the '_rootbuild_i386' job with
'_root_portbuild' including the new armhf and arm64 architecture.

The resulting jobs are named as follows:

 - lttng-tools_master_root_linuxbuild
 - lttng-tools_master_root_portbuild

This all means using a single template and having more consistent
naming.

Change-Id: I53a5a875bc76f128ff66000540c38b6be429e557
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>