fix NDK_UNAME to work more consistently by using Makefile exec, not sh exec

(:= is valid syntax in a Makefile)
update libsqlfs to get sqlfscat and sqlfsls
automatically build executable 'sqlfscat' for and

It is dynamically linked against libiocipher.so, so to use it you might
need to set LD_LIBRARY_PATH to include the path to the app's libs/ folder.