abuild: update output so multithreaded is decipherable

- add a 'quiet' mode that only prints important messages
- add vendor/mainboard to all strings printed

With quiet on, multithreaded looks like this:
skipping google/storm because we're missing compilers for (arm armv4 armv7)
iwill/dk8_htx built successfully. (took 5s)
jetway/j7f2 built successfully. (took 6s)
iwill/dk8x built successfully. (took 8s)
iwill/dk8s2 built successfully. (took 8s)
jetway/j7f4k1g5d built successfully. (took 10s)

With quiet off, single threaded now looks like this:
Building intel/emeraldlake2
Creating config file for intel/emeraldlake2...
    intel/emeraldlake2 (blobs, ccache)
intel/emeraldlake2 config created.
Compiling intel/emeraldlake2 image...
intel/emeraldlake2 built successfully. (took 5s)

And quiet off multithreaded looks like this:
Building iwill/dk8_htx
Creating config file for iwill/dk8_htx...
    iwill/dk8_htx (blobs, ccache)
intel/mohonpeak config created.
Compiling intel/mohonpeak image on 1 cpu...
intel/minnowmax config created.
--- snip ---
intel/mtarvon built successfully. (took 4s)
Building iwill/dk8s2
Creating config file for iwill/dk8s2...
    iwill/dk8s2 (blobs, ccache)
intel/mohonpeak built successfully. (took 5s)
Building iwill/dk8x

Change-Id: Ib7b9a625d77bb8e0663afc00d7133e415866ecec
Signed-off-by: Martin Roth <martin.roth@se-eng.com>
Reviewed-on: http://review.coreboot.org/7716
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>