dracut: let module handling function accept optional path option

dracut: let module handling function accept optional path option

Let the caller pass in the module path instead of try to find the module
path everytime. This helps optimize the overall runtime.

Test results (3 rounds) on Fedora 30 in KVM VM with 8 CPUs, 2G memory, HDD:

    $ time ./dracut.sh --local --quiet --hostonly --hostonly-cmdline --hostonly-i18n --hostonly-mode 'strict' -o 'plymouth dash resume ifcfg' --mount '/dev/mapper/fedora-root /sysroot xfs defaults' --no-hostonly-default-device -f initramfs.img
    Before the commit:
    real    0m11.782s  |  real    0m11.505s  |  real    0m11.958s
    user    0m9.169s   |  user    0m9.218s   |  user    0m9.327s
    sys     0m10.839s  |  sys     0m10.829s  |  sys     0m10.925s

    After this commit:
    real    0m9.866s  |  real    0m9.580s  |  real    0m9.638s
    user    0m9.048s  |  user    0m9.142s  |  user    0m9.120s
    sys     0m7.411s  |  sys     0m7.775s  |  sys     0m7.745s

Test result of building a ordinary image:

    $ time ./dracut.sh --local --quiet -f initramfs.img
    Before the commit:
    real    0m34.697s  |  real    0m34.371s  |  real    0m35.122s
    user    0m27.608s  |  user    0m27.524s  |  user    0m27.705s
    sys     0m22.341s  |  sys     0m22.032s  |  sys     0m22.246s

    After the commit:
    real    0m31.914s  |  real    0m31.006  |  real    0m31.289ss
    user    0m27.315s  |  user    0m27.324  |  user    0m27.290ss
    sys     0m19.051s  |  sys     0m18.916  |  sys     0m19.022ss

This will have an ~2s speed up.

Signed-off-by: Kairui Song <kasong@redhat.com>