LU-4009 osd-zfs: Add tunables to disable sync (DEBUG)

This is a debugging patch designed to determine how much of
a performance improvement can be expected once the ZIL is
implemented.

This is accomplished by replacing the call to txg_wait_synced(),
which will block waiting for a full pool sync, with a smaller
tunable delay.  This delay is intended to stand in for the time
it would have taken to synchronously write the dirty data to
the intent log.  However, be aware that no data is guaranteed
to be written and this patch is solely for performance analysis.

Two new tunables are introduced to control the delay, the
osd_object_sync_delay_us and osd_txg_sync_delay_us module options.
These values default to -1 which preserves the safe full sync
pool behavior.  Setting these values to zero or larger will
replace the pool sync with a delay of N microseconds.

The initial test results obtained by running sanityN test 16
(fsx) are encouraging.  If the zil_commit() time can be kept to
less than 10ms we should see a significant performance improvement.
These tests were run in a pristine centos 6.4 VM and the results
are averaged over four runs.

osd_txg_sync_delay_us	-1	-1	-1	-1	-1
osd_obj_sync_delay_us	-1	0	1000	10,000	100,000
---------------------------------------------------------------
SanityN test 16 (secs)	24.3	7.3	7.6	10.1	34.4

Change-Id: Iff9b66888edc79a5e1585fa3ce8377be068748f2
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
LU-3903 osd-zfs: Remove dead property handling code

The udmu_userprop_get_str(), udmu_userprop_set_str(), and
udmu_objset_name_get() functions are all currently unused.
Therefore this code is removed from the zfs osd.

If manipulation of zfs dataset properties is needed in the
future it can be done through the existing dsl_prop_get(),
dsl_prop_set_int(), and dsl_prop_set_string() interfaces.

This patch allows Lustre to cleanly build with versions
of zfs newer than 0.6.2.

Change-Id: I15b1ef8825dcdbed1572990d230776485d627457
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>