[MWRAPPER-147] mvnw.cmd fails to launch maven if username contains space

[sebthom]

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Addresses https://issues.apache.org/jira/browse/MWRAPPER-147

Executing mvnw on Windows where the user name contains space results mvnw failing to launch Maven:

> mvnw
'C:\Users\John' is not recognized as an internal or external command,
operable program or batch file.
Cannot start maven from wrapper

This is a big annoyance esp. for first time users of Maven wrapper who have no clue whats going on.

[cstamas]

@michael-o please take a look

[sebthom]

@slawekjaranowski can you please have a look?

[slawekjaranowski]

I don't use windows so can not confirm ... but looks ok