Fail hostnqn namespace add_host if subsystem host list does not contain this hostnqn

[rahullepakshi]

If a hostnqn intended to be masked with a namespace is not present at subsystem host list(when not "All hosts"), initiator having this hostnqn can never discover and connect to namespace above.

So we need to fail ns_add_host when

• subsystem containing this namespace is not visible to "All Hosts"(subsystem list has some hostnqns)
• hostnqn with ns_add_host command is not present in subsystem list above

Subystem_a has host list of "host_nqn_a, host_nqn_b"
ns_a is part of Subystem_a and is restrictive
When host_nqn_c is added part of masking to ns_a, initiator with host_nqn_c can never see this ns as subsystem is not masked with host_nqn_c

[gbregman]

This is a duplicate of issue #1127

[gbregman]

@rahullepakshi notice that I closed this issue as it's the same as issue #1127 which was fixed.