[explorer/machine_type] Simplify Linux + basic OpenBSD support.

By abstracting away vendor-dependent pattern matching for the linux code, we can
re-use that and be reasonably sure about OpenBSD machines being virtualised when
we can identify the undelrying virtualisation technology.
It remains to be solved how to tell if an OpenBSD machine is physical; in that
case previous cdist behaviour ("unknown") remains.

For NetBSD something similar to OpenBSD could be done, with different sysctls:
hw.machine and hw.model wary of adding those without testing though, so for
NetBSD previous cdist behaviour ("unknown") remains.
https://netbsd.gw.com/cgi-bin/man-cgi?sysctl+7.i386+NetBSD-9.0

cdist/conf/explorer/machine_type

@@ -22,6 +22,18 @@
 
 os=$("$__explorer/os")
 
+vendor_string_to_machine_type() {
+    for vendor in vmware bochs kvm qemu virtualbox bhyve; do
+        if echo "${1}" | grep -q -i "${vendor}"; then
+            if [ "${vendor}" = "bochs" -o "${vendor}" = "qemu" ]; then
+                vendor="kvm"
+            fi
+            echo "virtual_by_${vendor}"
+            exit
+        fi
+    done
+}
+
 case "$os" in
     "freebsd")
         # FreeBSD does not have /proc/cpuinfo even when procfs is used.
@@ -38,6 +50,18 @@ case "$os" in
         fi
     ;;
 
+    "openbsd")
+        # OpenBSD can also use the sysctl's: hw.vendor or hw.product.
+        # Note we can be reasonably sure about a machine being virtualised
+        # as long as we can identify the virtualisation technology.
+        # But not so much about it being physical...
+        # Patches are welcome / reach out if you have better ideas.
+        for sysctl in hw.vendor hw.product; do
+            # This exits if we can make a reasonable judgement
+            vendor_string_to_machine_type "$(sysctl -n "${sysctl}")"
+        done
+    ;;
+
     *)
         # Defaulting to linux for compatibility with previous cdist behaviour
 
@@ -54,7 +78,7 @@ fi
 
         if [ -r /proc/cpuinfo ]; then
             # this should only exist on virtual guest machines,
-    # tested on vmware, xen, kvm
+            # tested on vmware, xen, kvm, bhyve
             if grep -q "hypervisor" /proc/cpuinfo; then
                 # this file is aviable in xen guest systems
                 if [ -r /sys/hypervisor/type ]; then
@@ -63,32 +87,14 @@ if [ -r /proc/cpuinfo ]; then
                         exit
                     fi
                 else
-            if [ -r /sys/class/dmi/id/product_name ]; then
+                    for vendor_file in /sys/class/dmi/id/product_name \
-                if grep -q -i 'vmware' /sys/class/dmi/id/product_name; then
+                                       /sys/class/dmi/id/sys_vendor \
-                    echo "virtual_by_vmware"
+                                       /sys/class/dmi/id/chasis_vendor; do
-                    exit
+                        if [ -r ${vendor_file} ]; then
-                elif grep -q -i 'bochs' /sys/class/dmi/id/product_name; then
+                            # This exits if we can make a reasonable judgement
-                    echo "virtual_by_kvm"
+                            vendor_string_to_machine_type "$(cat "${vendor_file}")"
-                    exit 
-                elif grep -q -i 'virtualbox' /sys/class/dmi/id/product_name; then
-                    echo "virtual_by_virtualbox"
-                    exit 
-                fi
-            fi
-
-            if [ -r /sys/class/dmi/id/sys_vendor ]; then
-                if grep -q -i 'qemu' /sys/class/dmi/id/sys_vendor; then
-                    echo "virtual_by_kvm"
-                    exit
-                fi
-            fi
-
-            if [ -r /sys/class/dmi/id/chassis_vendor ]; then
-                if grep -q -i 'qemu' /sys/class/dmi/id/chassis_vendor; then
-                    echo "virtual_by_kvm"
-                    exit
-                fi
                         fi
+                    done
                 fi
                 echo "virtual_by_unknown"
                 exit