crypt: Skip /etc/crypttab if not present

Prevents following error message:

I: *** Including module: crypt ***
/usr/lib/dracut/modules.d/90crypt/module-setup.sh: line 31: /etc/crypttab: No such file or directory
LatArCyrHeb-16 as a default i18n font for Gentoo
network:ifup handle bootif style interfaces

e.g. ip=77-77-6f-6f-64-73:dhcp
systemd: add support for kmod static devnodes
dracut.spec: fix typo
base/dracut-lib.sh: check for /proc/cmdline existance
mdraid/mdmon-pre-shutdown.sh: removed unneeded code
url-lib/module-setup.sh: fixed grepping libcurl
crypt: Wait for udev to settle before unlocking disk

To eliminate a race condition that occurs when unlocking one device
depends on the result of unlocking a device before it, the crypt
module must wait for udev to settle between each unlock attempt.

Example

/etc/crypttab:

  keyfile /dev/md1 none luks
  sda4_crypt /dev/sda4 /dev/mapper/keyfile luks
  sdb4_crypt /dev/sdb4 /dev/mapper/keyfile luks

Without this patch, sometimes /dev/sda4 fails to unlock because udev
doesn't have time to create /dev/mapper/keyfile before it's needed.
base: hard depend on systemd, if system was started by systemd
dracut.sh: check for file existance before trying to read from it
systemd: include systemd-tempfiles
systemd/dracut-pre-trigger.service: run after systemd-tmpfiles-setup-dev
base/init.sh: create static device nodes with kmod
dracut.spec: add bcache and modsign module
TEST-10: double disk space
TEST-50-MULTINIC: change interface names to ens*
remove "< <(" syntax

bash seems to want /dev/fd in that case. dracut is sometimes called in
environments, where /proc and /dev are not mounted.
TEST-30-ISCSI: eth0 -> ens3
fips: cope with module aliases, when checking modules

Also do not fail, if module aliases try to load CPU specific modules
like crc32c_intel.