Virsh domfstrim test

```
NAME
    domfstrim - Invoke fstrim on domain's mounted filesystems.

  SYNOPSIS
    domfstrim <domain> [--minimum <number>] [<mountpoint>]

  DESCRIPTION
    Invoke fstrim on domain's mounted filesystems.

  OPTIONS
    [--domain] <string>  domain name, id or uuid
    --minimum <number>  Just a hint to ignore contiguous free ranges smaller than this (Bytes)
    [--mountpoint] <string>  which mount point to trim

Note: --mountpoint still not supported, so ignore it

```