zfs: rename zfs.go to zfs_common.go

Also add build-tags to ensure it is ignored on non-relevant archs.

Signed-off-by: Daniel Swarbrick <daniel.swarbrick@gmail.com>

collector/zfs_common.go

@@ -11,8 +11,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build !nozfs
+//go:build !nozfs && (freebsd || linux || solaris)
 // +build !nozfs
+// +build freebsd linux solaris
 
 package collector