lxd/project/permissions: Separate limits.disk validate from other keys in getInstanceLimits
lxd/project/permissions: Separate limits.disk validate from other keys in getInstanceLimits

And sort out the error formatting, using %q quoting, no line wrapping and modern error wrapping.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

stgraber/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,stgraber/lxd,hallyn/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,hallyn/lxd,hallyn/lxd,stgraber/lxd,lxc/lxd,stgraber/lxd,lxc/lxd