Stop using bash arrays for whitelisting in yum

Using -n for bash arrays was a little bit bad, and also resulted in
errors when running under set -u. Wean the yum element off the array
and switch to a straight string.

Change-Id: Ifd61fce7dadd5820022e9b2ab42020ba0cb71ce6
Merge "Stop using bash arrays for whitelisting in yum"