The original regex string for dd output goes wrong when
the dd speed is slow:
"""
2012-09-12 01:03:45: dd if=/dev/zero of=test_0zSfi bs=4k oflag=direct count=10000
2012-09-12 01:05:09: 10000+0 records in
2012-09-12 01:05:09: 10000+0 records out
2012-09-12 01:05:09: 40960000 bytes (41 MB) copied, 84.0859 s, 487 kB/s
"""

This patch update the regex string, making it can recognize more
speed format.

Changes from V3:
 * Fix incorrect placement of speed result convert line.
Changes from V2:
 * Update this patch against latest nfs_perf test script.
 * Use new utils_misc.standard_value api to convert result data.
Changelog from V1:
 * Convert all results in kB/s to MB/s.

CC: Wenli Quan <wquan@redhat.com>
CC: Xiaomei Gao <xigao@redhat.com>
CC: Yiqiao Pu <ypu@redhat.com>
Signed-off-by: NQingtang Zhou <qzhou@redhat.com>
Acked-by: NWenli Quan <wquan@redhat.com>