sanitycheck: Add --disable-size-report option

The segment size computation has value, but it's actually a very slow
process that parallizes poorly.  It seems to be bound by the Python
GIL doing the parsing, so never sees more than about 150% of CPU in
use even on wildly parallel systems.  And it takes about 75-80
seconds, which is 15-20% of the entire runtime of the test on that
box!

And the only "failure" case this can detect (unexpected sections in
the output file) is now a duplicate of the orphan section warning
we've since enalbled at the linker level.

This defaults to enabling the test to preserve behavior (as I don't
know where all the existing users of the size report are to change
them), but long term we might consider making "disabled" the default
and switching this to an --enable flag.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>