Quote unquoted file modes.

For compatibility with Puppet 4, which differentiates between strings
and integers, and file modes must be strings (since it could otherwise
be ambigous if a mode was specified as octal or decimal).

Found and fixed using puppet-lint for file, manually for concat::file.

(It would be tempting to use symbolic modes, e.g. 'u=rwx,go=rx', but
at least Puppet 2.7 does not remove setuid, setgid and sticky bits
correctly in this case.)

Signed-off-by: Thomas Bellman <bellman@nsc.liu.se>

This was originally commit 202d96229626 in nsc-puppet-utils.