fix(bootstrap_sdk): Remove toolchain build step, replaced by build_toolchains
fix(get_board_chost): Accept a list of boards to get_board_* funcs
fix(toolchain_util.sh): Move native->cross pkg translation to function

Will be useful in other places and seems better to hide the bash magic.
fix(common.sh): Use $SCRIPT_NAME as the default log prefix.

Seems useful with all the scripts-calling-scripts-turtles but very few
scripts explicitly set a prefix.
fix(catalyst.sh): Update catalyst build more aggressively.

Use 2*CPUs for the target load average but add load average throttling
to emerge in addition to make. Also work around how catalyst sets
FEATURES so we can disable extra locking for hopefully faster builds.
fix(toolchain_util.sh): Move cross-toolchain install code to common lib.

This will eventually be used by setup_board instead of the even more
complicated toolchain code provided by chromite.
fix(disk_layout_util.sh): Fix changing build_image's disk layout.

Previously the code in base_image_util.sh properly handled the disk
layout command line flag but the spaghetti code later on calls a
function from disk_layout_util.sh which only returned 'base' resulting
in a bit of a mess if something other than 'base' is used. Sync up the
two code paths to avoid that...
fix(board_options.sh): Move CHOST->ARCH mapping code.

Use the complete chost to portage arch mapping list from crossdev and
move the logic to toolchain_util.sh where it can be used by other
scripts.
fix(setup_board): Move to new toolchain_util.sh and eselect

The new toolchain utils define chost, portage profiles, and portage arch
per board. Replace the tricker logic from the old platform/dev repo and
switch to setting the profile with the standard eselect tool.

A few cleanups here and there, replacing echo with info and renames.
fix(build_packages): Don't redirect emerge output.

The stats upload has been removed so there is no longer a need to
capture the emerge output to parse the logged output. Remove a bit of
dead chromeos logic too.
fix(check_deps): Fix support for includes in ld.so.conf

The path passed to _ReadLdSoConf must start with a '/' which wasn't
happening since relpath returns a relative path.
fix(toolchain_util.sh): Switch from sudo_clobber to sudo tee

sudo_clobber is provided by common.sh which isn't included in the
catalyst environment so call sudo tee (what sudo_clobber does) directly
instead.
fix(build_toolchains): Upload packages to a new toolchain directory.

Currently we don't have a good way to upload packages from different
jobs to the same location. The 'Packages' index file is only generated
locally so the second upload would always win.
Merge pull request #131 from marineam/turtle-chain

Turtle chain: Building native compilers with cross compilers!