qemu.tests: Add a performance test of nfs with tcp protocol

Changes from v2:
 - Clean up temp files after testing.

Changes from v1:
 - Update mount option.
 - Create a new file for each block size testing.
 - Drop caches before running each test.
 - Re-format test results file.

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
qemu.tests.cfg: Create config file for nfs_perf script

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests.nfs_perf: Write test result to database

Save the write and read speed in database for nfs_perf.
It will be like this in database:
  nfs--$blk_size--[write|read]: $speed

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests.nfs_perf: Update the regex for dd output

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: Qingtang Zhou <qzhou@redhat.com>
Acked-by: Wenli Quan <wquan@redhat.com>
qemu.tests.nfs_perf: add version info in result file

impove the case in the scripts:
- The result file is named by nfs-perf.RHS
- Put the result into test.resultsdir
- Collect version info in result
- Format the result which can be used by regression.py

Change from v1:
- result file name is be set as a parameter
- replace parameter ver_cmd by kvm_userspace_ver_cmd

Change from v2:
- get_path to get the file path
- format the result which can be used by regression.py

Change from v3:
- modify speed result without unit

Signed-off-by: Xiaomei Gao <xigao@redhat.com>
Acked-by: Yiqiao Pu <ypu@redhat.com>