Replace bad style var=$(cat file) with read -r var < file

[aafeijoo-suse]

Following #1268, check what var=$(cat file) can be replaced with read -r var < file:

# grep -r -n --color "=\$(cat " modules.d
modules.d/01fips/fips.sh:85:    FIPSMODULES=$(cat /etc/fipsmodules)
modules.d/35network-legacy/net-genrules.sh:70:        bootdev=$(cat /tmp/net.bootdev)
modules.d/35network-legacy/dhcp-multi.sh:61:            pid=$(cat /tmp/dhclient."$netif".pid)
modules.d/35network-legacy/dhcp-multi.sh:119:            npid=$(cat /tmp/dhclient."$netif".pid)
modules.d/35network-legacy/ifup.sh:387:                        _hwaddr=$(cat "/sys/class/net/$slave/address")
modules.d/35network-legacy/ifup.sh:534:        BOOTDEV=$(cat /tmp/net.bootdev)
modules.d/40network/netroot.sh:29:            mac=$(cat "$i")
modules.d/40network/net-lib.sh:825:        && _name_assign_type=$(cat "/sys/class/net/$_netif/name_assign_type" 2> /dev/null)
modules.d/40network/net-lib.sh:860:        _name_assign_type=$(cat "/sys/class/net/$_netif/name_assign_type")
modules.d/45ifcfg/write-ifcfg.sh:154:    uuid=$(cat /proc/sys/kernel/random/uuid)
modules.d/80cms/cms-write-ifcfg.sh:26:    uuid=$(cat /proc/sys/kernel/random/uuid)
modules.d/90dm/dm-shutdown.sh:20:            devname=$(cat /sys/block/"${dev}"/dm/name)
modules.d/95fcoe/fcoe-up.sh:21:iflink=$(cat /sys/class/net/"$netif"/iflink)
modules.d/95fcoe/fcoe-up.sh:22:ifindex=$(cat /sys/class/net/"$netif"/ifindex)
modules.d/95iscsi/module-setup.sh:81:        is_boot=$(cat "$flash"/is_boot_target)
modules.d/95iscsi/module-setup.sh:84:            iscsi_initiator=$(cat /sys/class/iscsi_host/"${iscsi_host}"/initiatorname)
modules.d/95iscsi/module-setup.sh:96:                    iscsi_address=$(cat "${conn}"/persistent_address)
modules.d/95iscsi/module-setup.sh:97:                    iscsi_port=$(cat "${conn}"/persistent_port)
modules.d/95iscsi/module-setup.sh:102:                    iscsi_initiator=$(cat "${d}"/"${iscsi_session}"/initiatorname)
modules.d/95iscsi/module-setup.sh:103:                    iscsi_targetname=$(cat "${d}"/"${iscsi_session}"/targetname)
modules.d/95iscsi/iscsiroot.sh:62:        retry=$(cat /tmp/session-retry)
modules.d/95lunmask/fc_transport_scan_lun.sh:23:    TARGET=$(cat /sys"$DEVPATH"/scsi_target_id)
modules.d/95lunmask/module-setup.sh:24:            _wwpn=$(cat "${_classdev}"/port_name)
modules.d/95lunmask/module-setup.sh:34:            _sas_address=$(cat "${_classdev}"/sas_address)
modules.d/95lunmask/module-setup.sh:49:        scan_type=$(cat /sys/module/scsi_mod/parameters/scan)
modules.d/95lunmask/sas_transport_scan_lun.sh:23:    TARGET=$(cat /sys"$DEVPATH"/scsi_target_id)
modules.d/95nfs/nfsroot-cleanup.sh:5:[ -f /tmp/nfs.rpc_pipefs_path ] && rpcpipefspath=$(cat /tmp/nfs.rpc_pipefs_path)
modules.d/95nvmf/module-setup.sh:21:                trtype=$(cat "$d"/transport)
modules.d/95nvmf/module-setup.sh:78:                trtype=$(cat "$d"/transport)
modules.d/95nvmf/module-setup.sh:101:        _hostnqn=$(cat /etc/nvme/hostnqn)
modules.d/95nvmf/module-setup.sh:105:        _hostid=$(cat /etc/nvme/hostid)
modules.d/95rootfs-block/mount-root.sh:54:            fsckoptions=$(cat "$NEWROOT"/fsckoptions)
modules.d/97masterkey/masterkey.sh:53:    KEYBLOB=$(cat "${MASTERKEYPATH}")
modules.d/98ecryptfs/ecryptfs-mount.sh:39:    KEYBLOB=$(cat "${ECRYPTFSKEYPATH}")
modules.d/98integrity/evm-enable.sh:53:    KEYBLOB=$(cat "${EVMKEYPATH}")
modules.d/98usrmount/mount-usr.sh:29:        _fsckoptions=$(cat "$NEWROOT"/fsckoptions)
modules.d/99base/dracut-lib.sh:935:                _ctty=$(cat /sys/class/tty/$_ctty/active)
modules.d/35connman/netroot.sh:29:            mac=$(cat "$i")
modules.d/90dmsquash-live-autooverlay/create-overlay.sh:50:        partition=$(cat ${rootDeviceSysfsPath}/partition)
modules.d/90dmsquash-live-autooverlay/create-overlay.sh:55:    readonly=$(cat ${rootDeviceSysfsPath}/ro)