Support building with docker.

Signed-off-by: Anthony Romano <anthony.romano@coreos.com>

src/configure

@@ -46,7 +46,7 @@ hid_card_change=no
 factory_reset=no
 
 # Revision number
-if test -e ../.git; then
+if which git >/dev/null 2>&1 && test -e ../.git; then
   REVISION=`git describe --dirty="-modified"` 
 else
   REVISION=`cat ../VERSION`