Use binary-deps.d for dracut ramdisks

Instead of hard-coding a list of binaries to include in the dracut
ramdisk, use the existing binary-deps.d functionality to provide a
list.  This will allow other ramdisks (such as discovery) to add
the binaries they need.

Change-Id: Ib7ffa15e08db1cc45e93a8f2a5c01369772c93ff
Unset trap before dracut ramdisk build script exits

A similar change was needed in the normal ramdisk element as part
of ae928057bd2fc2205c91bf052d5503de64f9ea69 to avoid running
cleanup immediately after the ramdisk build completes.

Change-Id: Ia96e2d8011b88ed96cc6727914c5a5d2dea59757
Merge "Use binary-deps.d for dracut ramdisks"
Merge "Unset trap before dracut ramdisk build script exits"