rename and change reference file creation behavior

Just rename existing /etc/default/kdump-tools to .ref

Signed-off-by: Louis Bouchard <louis.bouchard@canonical.com>
Minor fix and syntax modification

Signed-off-by: Louis Bouchard <louis.bouchard@canonical.com>
Implement configuration file modification

Do sanity checks and modify the configuration file according
to the running tests

Signed-off-by: Louis Bouchard <louis.bouchard@canonical.com>
DEP8 fixup

Signed-off-by: Louis Bouchard <louis.bouchard@canonical.com>