build: support for SCREWD product builds (EXPERIMENT)

note:
 - adapted from CM for SCREWD use

If building a screwd_* product, skip crawling the filesystem for
AndroidProduct makefiles (and, of course, parsing their contents)
and aim directly for the vendor/screwd/products/<product> device configuration

Change-Id: I2a5e70dda973a6fcdbba0d5e26b35b99d3f1aea2
print SCREWD_VERSION in build config

Change-Id: Iead654e30798a11e636ec743683f3431d14a858c