Updating init scripts to have more robust grepping

The previous pattern could accidentally match on things like
'real_root=ZFS=node02-zp00/ROOT/rootfs' due to the 'ZFS=no'
substring.

Signed-off-by: Matthew Thode <mthode@mthode.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1837