ctr: parse mount options with embedded = character
ctr: parse mount options with embedded = character

FreeBSD mount options may have embedded = characters.  For example,
devfs(5) supports the `ruleset` option which can be passed as
`ruleset=4` to indicate that ruleset 4 should be used.

Signed-off-by: Samuel Karp <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@samuelkarp.com>

thaJeztah/containerd,estesp/containerd,dmcgowan/containerd,mikebrow/containerd,containerd/containerd,thaJeztah/containerd,mikebrow/containerd,estesp/containerd,containerd/containerd,dmcgowan/containerd