tests: specify the image format when possible

When possible, make the disk image format explicit when invoking tools
or using add-drive. This avoids warnings from qemu about the unspecified
format for the image, and also makes qemu slightly faster (skipping the
disk image probing).
Tests checking the image probing are not touched.

This changes also:
- old-style invocations of tools (`$tool $filename`) into new style
  (`$tool -a $filename`)
- add-drive-ro/add-drive-with-if guestfish commands into add/add-drive
  with explicit readonly/iface arguments

There should be no change in the tests results.

tests/md/test-inspect-fstab-md.sh

@@ -32,7 +32,7 @@ rm -f inspect-fstab-md-{1,2}.img inspect-fstab-md.fstab inspect-fstab-md.output
 cp ../../test-data/phony-guests/fedora-md1.img inspect-fstab-md-1.img
 cp ../../test-data/phony-guests/fedora-md2.img inspect-fstab-md-2.img
 
-guestfish -i inspect-fstab-md-[12].img <<'EOF' | sort > inspect-fstab-md.output
+guestfish -i --format=raw -a inspect-fstab-md-1.img --format=raw -a inspect-fstab-md-2.img <<'EOF' | sort > inspect-fstab-md.output
   exists /boot/grub/grub.conf
 EOF
 
@@ -47,13 +47,13 @@ cat <<'EOF' > inspect-fstab-md.fstab
 /dev/md/boot /boot ext2 default 0 0
 EOF
 
-guestfish -a inspect-fstab-md-1.img -a inspect-fstab-md-2.img <<'EOF'
+guestfish --format=raw -a inspect-fstab-md-1.img --format=raw -a inspect-fstab-md-2.img <<'EOF'
   run
   mount /dev/VG/Root /
   upload inspect-fstab-md.fstab /etc/fstab
 EOF
 
-guestfish -i inspect-fstab-md-[12].img <<'EOF' | sort > inspect-fstab-md.output
+guestfish -i --format=raw -a inspect-fstab-md-1.img --format=raw -a inspect-fstab-md-2.img <<'EOF' | sort > inspect-fstab-md.output
   exists /boot/grub/grub.conf
 EOF