bitbake: toaster: enable SSH-based remote build support

bitbake: toaster: enable SSH-based remote build support

We enable support for starting builds on remote machines
through SSH. The support is limited to poky-based distributions.

We refactor localhost build support and we update
bldcontrol application tests to uniformely test the APIs
of localhost and SSH build controllers.

[YOCTO #6240]

(Bitbake rev: c2ad9c9bb83f61c171434324df8c4d5ee655a556)

Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>