Resolves #15537 malformed mdadm.conf lines

This resolves a few different issues with the save_config method of salt.modules.mdadm:
* If multiple mdadm raid volumes are present they are properly recorded on seperate lines in the mdadm.conf
* if a given volume was already represented in mdadm.conf it's ARRAY line is updated instead of having a duplicate blindly appended
* The logic for the ubuntu bugfix workaround was also modified to use a case insensitive regex replace