Numerous bugfixes, and enhancements

Changed logs to *.txt (00-run-all-scripts.cmd)
Replaced hardcoded 'a:\' with %~dp0 (00-run-all-scripts.cmd)
Moved a:\ to end of search path (_download.cmd)
Fixed inability to find wget.exe in path (_download.cmd)
Fixed typo in download code (openssh.cmd)
Only turn echo off if PACKER_DEBUG is not defined (script/*.bat)
Removed bogus goto label ':finish' (vmtools.bat)