This commit adds a logging verbosity level flag to extract_ir.py and the
appropriate plumbing/implementation in extract_ir_lib.py. This is
primarily motivated by these errors coming up quite often in non-trivial
builds (as it is fairly often there is some assembly or some flags don't
get passed around somewhere) and not providing a very high signal to
noise ratio, especially when used as a library against a bunch of
projects at once.

- Don't change logging verbosity back to info to print the status
  message if the verbosity has been set lower.

- Log subprocess output directly rather than having subprocess write
  directly to STDOUT/STDERR.

- Switch to using subprocess.check_output