Hi Kathy,
TNX for sharing the root cause!
For Community ref: at least Moodle dataroot should be writable but if you like to manage plug-ins install&update even from the web interface you should add some write permissions in some of the folders of the web root.
A good reference - at least, an excellent starting point - for SELinux IMHO is: http://blog.mrverrall.co.uk/2015/10/moodle-on-centos-and-red-hat-7.html
HTH,
Matteo