gpt-auto-generator: disable gpt auto logic for swaps if at least one is defined in...

gpt-auto-generator: disable gpt auto logic for swaps if at least one is defined in fstab

If a swap partition is created on a disk using GPT then the unit generated by
the gpt-generator can shadow the one generated by the fstab-generator.

This can be an issue if the fstab entry for the swap has options since they are
simply ignored if PID1 decides to use the unit created by the gpt-generator
since this unit carries no information about the swap options.

This patch simply disables the GPT auto logic for swaps if at least one entry
for swap is defined in /etc/fstab.

Fixes: #6192