check_vol_slaves() in dracut-functions.sh does not strip whitespaces from volume group name

Issue

• When one run dracut --debug following appears:

//usr/lib/dracut/dracut-functions.sh@688(check_vol_slaves): lvm lvs --noheadings -o vg_name /dev/mapper/os-root
/usr/lib/dracut/dracut-functions.sh@688(check_vol_slaves): _vg='  os  '
//usr/lib/dracut/dracut-functions.sh@690(check_vol_slaves): printf '%s\n' '  os  '
/usr/lib/dracut/dracut-functions.sh@690(check_vol_slaves): _vg='  os  '
/usr/lib/dracut/dracut-functions.sh@691(check_vol_slaves): [[ -n   os   ]]
//usr/lib/dracut/dracut-functions.sh@684(check_vol_slaves): lvm vgs --noheadings -o pv_name '  os  '
/usr/lib/dracut/dracut-functions.sh@699(check_vol_slaves): return 1

• There're whitespaces that cause check_vol_slaves() to fail.