Fix command for finding and deleting old backups

[christarazi]

Previously, the find command would list all the *.img files because order of the operators were not correct. What the command translated to is:

Find all the files with the name *.img. If nothing was found, then find all the files with the name *.gz that have been modified over RETENTIONPERIOD hours.

For me, this listed all my .img files and was deleting all them of them. I was wondering why the script never created any backups...they were being deleted right away.

What we want is:

Find all the files modified over RETENTIONPERIOD hours, with the name *.img OR *.gz.

This fixed the problem for me.