completion: split dnf_commands_helper() command and options

The completion helper command is a bit long.  Split the command and
options into local variables to improve readability.

Closes: #894
Approved by: m-blaha

etc/bash_completion.d/dnf

@@ -120,7 +120,9 @@ _dnf_set_python_exec()
 
 _dnf_commands_helper()
 {
-    echo "$( ${__dnf_python_exec} -c "import sys; from dnf.cli import completion_helper as ch; ch.main(sys.argv[1:])" "$@" -d 0 -q -C --assumeno --nogpgcheck 2>/dev/null </dev/null )"
+    local helper_cmd="import sys; from dnf.cli import completion_helper as ch; ch.main(sys.argv[1:])"
+    local helper_opts="-d 0 -q -C --assumeno --nogpgcheck"
+    echo "$( ${__dnf_python_exec} -c "$helper_cmd" "$@" $helper_opts 2>/dev/null </dev/null )"
 }
 
 _dnf_is_path()