m4: Check for sanlock_write_lockspace

m4: Check for sanlock_write_lockspace

Currently, we are checking for sanlock_add_lockspace_timeout
which is good for now. But in a subsequent patch we are going to
use sanlock_write_lockspace (which sets an initial value for io
timeout for sanlock). Now, there is no reason to check for both
functions in sanlock library as the sanlock_write_lockspace was
introduced in 2.7 release and the one we are currently checking
for in the 2.5 release. Therefore it is safe to assume presence
of sanlock_add_lockspace_timeout when sanlock_write_lockspace
is detected.

Moreover, the macro for conditional compilation is renamed to
HAVE_SANLOCK_IO_TIMEOUT (as it now encapsulates two functions).

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>