Add bsopts flag

tgtadm: accept and pass bsopts
spc.c: permit bsopts as a legal option
target.c: accept bsopts=
tgtd.h: add char *bsopts to bs_init signature
bs_*.c: add char *bsopts as second arg to bs_init function
tgt-admin: process bsopts
doc/tgtadm.8.xml: add doc for bsopts and example

Signed-off-by: Dan Mick <dan.mick@inktank.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>