{Misc.} Change name of Bash completion function (Azure#23287)

Author: elyscape

az.completion

@@ -1,4 +1,4 @@
-_python_argcomplete() {
+_az_python_argcomplete() {
     local IFS=$'\013'
     local SUPPRESS_SPACE=0
     if compopt +o nospace 2> /dev/null; then
@@ -18,4 +18,4 @@ _python_argcomplete() {
         compopt -o nospace
     fi
 }
-complete -o nospace -o default -o bashdefault -F _python_argcomplete "az"
+complete -o nospace -o default -o bashdefault -F _az_python_argcomplete "az"