Hi,

I'm getting a kind of undefined behavior where parenthesis seem handled in a strange way. On display, it has a conflict between parenthesis of the option, and nested parenthesis within a metavar.

## Reproduction script

```
import argparse

def main():
    parser = argparse.ArgumentParser()

    group = parser.add_mutually_exclusive_group(required=True)

    group.add_argument("-p", "--path", metavar="/var/www/html", 
            help="DocumentRoot path")
    group.add_argument("-r", "--reverse", metavar="http)s(://Host:Port",
            help="Reverse proxy address")

    parser.add_argument("--last-args")
    return parser.parse_args()

main()
```

## Output of help menu
```
usage: crash.py [-h] (-p /var/www/html | -r http)s://Host:Port [--last-args LAST_ARGS]
```

## Expected behavior
```
usage: crash.py [-h] (-p /var/www/html | -r http)s(://Host:Port) [--last-args LAST_ARGS]
```