CB-6668: Use <description> for "plugin ls" when <name> is missing.

Plugin listing looks like the output below. The last column is now
plugin.name || plugin.description

$ cordova plugin ls
com.test.plugman 0.1.1 "plug_test"
org.apache.cordova.file 1.1.0 "File"
org.apache.cordova.statusbar 0.1.3 "StatusBar"