Add --use-fuse switch to kvm-test --install so it can run as non-root

Passing --use-fuse to scripts/kvm-test.py allows to run as non-root.

It requires installation of the package fuseiso so the switch is
disabled by default.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

scripts/kvm-test.py

@@ -174,6 +174,8 @@ parser.add_argument('--install', default=False, action='store_true',
                     iso, use a base iso, or reuse previous test iso''')
 parser.add_argument('--boot', default=False, action='store_true',
                     help='boot test image')
+parser.add_argument('--use-fuse', default=False, action='store_true',
+                    help="use FUSE to mount ISO (doesn't require root)")
 
 
 def parse_args():
@@ -229,12 +231,23 @@ def noop(path):
 
 
 @contextlib.contextmanager
-def mounter(src, dest):
-    run(f'sudo mount -r {src} {dest}')
+def mounter(src, dest, use_fuse: bool = False):
+    commands_with_fuse = (
+        ["fuseiso", src, dest],
+        ["fusermount", "-u", dest],
+    )
+    commands_without_fuse = (
+        f'sudo mount -r {src} {dest}',
+        f'sudo umount {dest}',
+    )
+
+    mount, unmount = commands_with_fuse if use_fuse else commands_without_fuse
+
+    run(mount)
     try:
         yield
     finally:
-        run(f'sudo umount {dest}')
+        run(unmount)
 
 
 def livefs_edit(ctx, *args):
@@ -426,7 +439,7 @@ def install(ctx):
             run(f'qemu-img create -f qcow2 {ctx.target} {ctx.args.disksize}')
 
         if len(appends) > 0:
-            with mounter(iso, mntdir):
+            with mounter(iso, mntdir, ctx.args.use_fuse):
                 # if we're passing kernel args, we need to manually specify
                 # kernel / initrd
                 kvm.extend(('-kernel', f'{mntdir}/casper/vmlinuz'))