kernel plugin _make_initrd fails to add given modules

The kernel plugin does not add given modules to the initrd. In the given snapcraft.yaml "ahci" is not added to initrd. This happens because all kernel-initrd-modules are added the the commandline:

modprobe -n --show-depends -d /test/parts/kernel/install -S 4.4.5-test+ squashfs ahci

instead of running modprobe extra for each module:
modprobe -n --show-depends -d /test/parts/kernel/install -S 4.4.5-test+ squashfs
modprobe -n --show-depends -d /test/parts/kernel/install -S 4.4.5-test+ ahci

name: test-kernel
version: 4.4.0
summary: ubuntu xenial kernel
description: A standard kernel
type: kernel

parts:
  kernel:
    plugin: kernel
    source: git://kernel.ubuntu.com/ubuntu/ubuntu-xenial.git
    source-type: git
    source-branch: Ubuntu-4.4.0-14.30
    kdefconfig: [defconfig]
    kconfigs:
      - CONFIG_LOCALVERSION="-test"
      - CONFIG_DEBUG_INFO=n
      - CONFIG_SQUASHFS=m
      - CONFIG_SQUASHFS_XZ=y
      - CONFIG_USB_XHCI_HCD=y
      - CONFIG_R8169=m
      - CONFIG_SECURITY_APPARMOR=y
      - CONFIG_SECURITY_APPARMOR_BOOTPARAM_VALUE=1
      - CONFIG_SECURITY_APPARMOR_UNCONFINED_INIT=y
      - CONFIG_SECURITY_APPARMOR_HASH=y
      - CONFIG_SECURITY_APPARMOR_HASH_DEFAULT=y
      - CONFIG_DEFAULT_SECURITY_APPARMOR=y
      - CONFIG_DEFAULT_SECURITY="apparmor"
      - CONFIG_ATA=y
      - CONFIG_SATA_AHCI=m
      - CONFIG_SATA_AHCI_PLATFORM=m
    kernel-initrd-modules:
      - squashfs
      - ahci

Example resolution would be
FROM:
    def _make_initrd(self):
        logger.info('Generating driver initrd for kernel release: {}'.format(
            self.kernel_release))

        initrd_unpacked_path = self._unpack_generic_initrd()

        if self.options.kernel_initrd_modules:
            modprobe_out = self.run_output([
                'modprobe', '-n', '--show-depends', '-d', self.installdir,
                '-S', self.kernel_release] +
                self.options.kernel_initrd_modules)
            modprobe_outs = modprobe_out.split(os.linesep)
        else:
            modprobe_outs = []

TO:
    def _make_initrd(self):
        logger.info('Generating driver initrd for kernel release: {}'.format(
            self.kernel_release))

        initrd_unpacked_path = self._unpack_generic_initrd()

        modprobe_outs = []
        for initrd_module in self.options.kernel_initrd_modules:
            modprobe_out = self.run_output([
                'modprobe', '-n', '--show-depends', '-d', self.installdir,
                '-S', self.kernel_release] + [initrd_module])
            modprobe_outs.append(modprobe_out)