LU-15913 tests: add rename stress test via racer

LU-15913 tests: add rename stress test via racer

Add a rename stress test using the racer framework.  Use
mrename if found, to avoid stat and allow directory rename.
Sometimes create and rename files to/from subdirectories.

Run e2fsck after every run to confirm filesystem structure.

Allow tunable parameters via environment variables so they
can be set via Test-Parameters.  Parameters can be set on
different nodes via variables CLIENT_LCTL_SETPARAM_PARAM,
MDS_LCTL_SETPARAM_PARAM, OSS_LCTL_SETPARAM_PARAM.

Test-Parameters: trivial testlist=racer env=ONLY=2 mdtcount=2
Test-Parameters: testlist=racer env=ONLY=2 mdscount=2 mdtcount=4
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I2ae034b864a5ccb8a59bf7028d22cd67c643f51f