(PUP-2364) Fix usage of puppet vardir setting Win2003

• Previous acceptance tests were using the Beaker puppetvardir setting. On Windows, this uses cygpath to resolve to an 8.3 style name that can be used in shell commands without quoting. By changing the acceptance tests to use the Puppet configuration value instead, a Windows long file name will be used instead of the 8.3 style. This does not affect any OS newer than Windows 2003R2, because the vardir path does not contain spaces. On Windows 2003R2, vardir is rooted in C:\Documents and Settings\ which means it must be quoted when using it in shell commands within Cygwin. Verified that other shells like Bash (on Linux and AIX) can still work properly quoted, and made changes to the acceptance tests to quote when in doubt.
• Fixed string interpolation in acceptance test 6541 for invalid file bucket files.