xe autocompletion: Exclude previously entered parameters before deciding

whether to show optionality of the parameters

Fixes the bug when optionality of parameters would be shown when all the
remaining parameters were of the same category, autocompleting the noise:
```
$ xe vm-param-get <TAB>
OPTIONAL: database:    REQUIRED: param-name=
OPTIONAL: param-key=   REQUIRED: uuid=

$ xe vm-param-get param-name=SMTH uuid=SMTH <TAB> <- automatically completes to
$ xe vm-param-get param-name=SMTH uuid=SMTH OPTIONAL:
```

Now works as intended:
```
$ xe vm-param-get param-name=SMTH uuid=SMTH <TAB>
database:   param-key=
```

Signed-off-by: Andrii Sultanov <[email protected]>

ocaml/xe-cli/bash-completion

@@ -814,15 +814,14 @@ set_completions()
     if [[ $REQD_OPTIONAL_PARAMS == 1 ]]; then
         local reqd_params=$( __preprocess_suggestions "$REQD_PARAMS" )
         local opt_params=$( __preprocess_suggestions "$OPT_PARAMS" )
+        if [[ "$excludes" ]]; then
+            reqd_params=$(echo "$reqd_params" | eval "grep -v $excludes")
+            opt_params=$(echo "$opt_params" | eval "grep -v $excludes")
+        fi
         if [[ "$reqd_params" && "$opt_params" ]]; then
             __xe_debug "showing optional/required parameters"
             SHOW_DESCRIPTION=1
 
-            if [[ "$excludes" ]]; then
-                reqd_params=$(echo "$reqd_params" | eval "grep -v $excludes")
-                opt_params=$(echo "$opt_params" | eval "grep -v $excludes")
-            fi
-
             for word in $reqd_params; do
                 __add_completion "$word" "REQUIRED" "$max_cmd_length"
             done