Moving guava from src/lib/guava to src/lib/salad

include/lib/salad/guava.h

src/box/CMakeLists.txt

src/ffisyms.cc

src/lib/CMakeLists.txt

src/lib/salad/CMakeLists.txt

src/lib/salad/guava.c

test/unit/CMakeLists.txt

test/unit/guava.c