[t:2499] Allow test program to set loader's scale_factor. Improve loader-cleanup-test to exercise with different combinations of size_factor, ENOSPC from toku_os_write(), and abort_on_poll. Command line options are used to exercise known bugs.

git-svn-id: file:///svn/toku/tokudb@20109 c7de825b-a66e-492c-adef-691d508d4ae1