fix(toolchain_util): Move toolchain build-dep code from catalyst.

Now this code can be shared with setup_board. Only required if
setup_board is called with --nousepkg which is rare to never but feels
like the correct thing to do. Alternatively setup_board could always
use binary packages (as it basically does now).
fix(setup_board): Hide --getbinpkg, it isn't useful for setup_board.

A new board build root always starts with an empty package cache so if
binary packages are enabled downloading is required. The distinction can
be useful for passing to update_chroot since its cache isn't impacted so
the flag remains, just among the less used hidden ones.
fix(toolchain_util.sh): Don't build via crossdev if pkgs are up to date.

When calling update_chroot with --nousepkg it is silly to always force a
rebuild of the cross toolchain. Change the test to work regardless of
whether binary packages are enabled by checking if anything needs to be
built from source.
fix(toolchain_util.sh): Fix variable name conflicts.

Although it didn't seem to be causing any bugs the global variables in
toolchain_util conflicted with some names used elsewhere. Clean that up
by adding an S to the array names that didn't already have one.
fix(toolchain_util.sh): Replace TOOLCHAIN_BINONLY with a function.

The new function supports generating arguments for cross toolchain
packages in addition to native ones.
fix(setup_board): Install board build root toolchains via emerge!
fix(build_image_util.sh): Move image install mask to portage profile.

Reduce the spaghetti config a bit...
fix(common.sh): Remove some dead code.
fix(base_image_util.sh): Install glibc and gcc libs via emerge.
fix(build_image): Add --fast to control use of parallel_emerge

This makes it possible to toggle parallel_emerge just as other scripts
do. In other scripts update the help string to be more specific, the
--jobs option can be used to control parallelism.
fix(*): Change default for --jobs to $NUM_JOBS

This makes parallelism behavior between parallel_emerge and emerge
consistent. NUM_JOBS is defined as the number of CPUs by common.sh
Merge pull request #138 from marineam/turtle-chain

Turtle chain