Fix string parsing

Fix string parsing

Fix propagation of -e option - pass it via internal shell variable.
Fix parsing of /proc/mounts files (don't check for substrings).
 as reported by O.Mangold with suggested patch:
 https://www.redhat.com/archives/linux-lvm/2012-February/msg00030.html
Properly pass arguments with spaces ("$@")
Add validation for YES and EXTOFF variable content.