_ios_dump_thread is not terminated by the function
_ios_destroy_dump_thread when the diagnostic interval is set
to 0 (which means disable auto dumping).

During reconfigure, if the value changes from 0 to another
then the thread is started, but on reconfiguring this to 0
the thread is not being terminated.

Further, if the value is changed from 0 to X to 0 to Y, where
X and Y are 2 arbitrary duration numbers, the reconfigure
code ends up starting one more thread (for each change from
0 to a valid interval).

This patch fixes the same by terminating the thread when the
value changes from non-zero to 0.

NOTE: It would seem nicer to use conf->dump_thread and check
its value for thread presence etc. but there is no documented
invalid value for the same, and hence an invalid check is not
feasible, thus introducing a new running bool to determine the
same.

Fixes: bz#1598548
Change-Id: I3e7d2ce8f033879542932ac730d57bfcaf14af73
Signed-off-by: ShyamsundarR <srangana@redhat.com>