Add better support for multiple initramfs

Fix a problem that we can't insert kernel modules in the early hooks for network and any other things.
We can not use the init hooks for inserting kernel modules because /proc/modules isn't available at this stage.
Also wait for sshd only if rescueshell has never occur and don't wait remaining time for sshd_wait if we send resume-boot from remote shell.

This changes allow me to use standalone better-initramfs with separated kernel modules and with following boot-update config:

"Funtoo Linux better-initramfs standalone+modules" {
    kernel kernel[-v]
    initrd  = initramfs.standalone.cpio.gz
    initrd += initramfs.modules.only.cpio.gz
    initrd += initramfs.remote.cpio.gz
    initrd += initramfs.prompt.cpio.gz
    initrd += initramfs.strace.cpio.gz
    initrd += initramfs.htop.cpio.gz
    #params += initramfsdebug
    #params += rootdelay=10
    params += binit_net_if=eth0
    params += binit_net_addr=10.9.1.27/24
    params += binit_net_gw=10.9.1.1
    params += sshd_wait=20
    params += sshd
    params += rw
}

P.S.: boot-update also need this patch https://github.com/nordaux/boot-update/commit/2e8d4850de998a1d4b9ab1ec33112f0655c32453