mdmon: Stop parsing duplicate options

mdmon: Stop parsing duplicate options

Introduce new function is_duplicate_opt() to check if given option
was already used and prevent setting it again along with an error
message.

Move parsing above in_initrd() check to be able to detect --offroot
option duplicates.

Now help option is executed after parsing to prevent executing commands
like: 'mdmon --help --ndlksnlksajndfjksndafasj'.

Signed-off-by: Lukasz Florczak <lukasz.florczak@linux.intel.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>