BUGFIX - globbed --boot-files are not copied properly

Referenced in Issue #364, where a --boot-file named Foo would be
copied into the tftproot/images/distro directory as FooFoo. As
noted in that issue, this was caused by commit 3c53042 which seems
to assume that all boot files will be globs.
Merge pull request #446 from cobbler/issue_364

BUGFIX - globbed --boot-files are not copied properly