sandbox: Refactored/enhanced script execution
further wip on new script engine
REF sandbox: sane control flow
new script runner: log multiplexing
REF sandbox.py -> run_job.py
Refactor configuration class

Instead of InifileConfiguration class, simply parse the inifile once
with a schema and pass around resulting dict. This was done to make
it easy to serialize the configuration and put it in HDIST_CONFIG.
REF major refactor to make Builder use new run_job

The reason this got a bit involved is that in order to localize
environment setup to run_job only, Builder now inserts new commands
for unpacking 'sources' and writing 'files'.
REF recipes and profile building refactored to new run_job.py
mystack.py
BUG fix hdist clearbuilds
DOC run_job fixes
REF remove special case+transforms for 'sources' and 'files'
recipes: prepend host package names with "host-"
more silent logging
REF execute_files_dsl -> hashdist.core.build_tools
REF builder.compress -> fileutils.gzip_compress
REF flatten hashdist.core.build_store package