schroot: fix indentation, variable scope/enclosure

puppet-lint printed some warnings:

WARNING: top-scope variable being used without an explicit namespace on line 75
WARNING: indentation of => is not properly aligned (expected in column 10, but found it in column 11) on line 45
WARNING: indentation of => is not properly aligned (expected in column 10, but found it in column 11) on line 46
WARNING: indentation of => is not properly aligned (expected in column 10, but found it in column 11) on line 49
WARNING: indentation of => is not properly aligned (expected in column 10, but found it in column 11) on line 50
WARNING: indentation of => is not properly aligned (expected in column 11, but found it in column 10) on line 54
WARNING: variable not enclosed in {} on line 59