LU-13417 test: use mkdir_on_mdt0() in misc tests

LU-13417 test: use mkdir_on_mdt0() in misc tests

Replace mkdir with mkdir_on_mdt0() if directory needs to be created
on MDT0 in following tests:
* conf-sanity
* lustre-rsync-test
* ost-pools
* replay-ost-single
* replay-single
* replay-vbr
* sanity-hsm
* sanity-pcc
* sanity-quota
* sanity-sec

Lustre-change: https://review.whamcloud.com/43491
Lustre-commit: de62c8c7ef5d627da872260686d9279cbb60736e

Test-Parameters: trivial mdscount=2 mdtcount=4 testlist=conf-sanity
Test-Parameters: mdscount=2 mdtcount=4 testlist=lustre-rsync-test
Test-Parameters: mdscount=2 mdtcount=4 testlist=ost-pools
Test-Parameters: mdscount=2 mdtcount=4 testlist=replay-ost-single
Test-Parameters: mdscount=2 mdtcount=4 testlist=replay-single,replay-vbr
Test-Parameters: mdscount=2 mdtcount=4 testlist=sanity-hsm,sanity-pcc
Test-Parameters: mdscount=2 mdtcount=4 testlist=sanity-quota
Test-Parameters: mdscount=2 mdtcount=4 testlist=sanity-sec
Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I96369f25982558a1dac7f4f7fe80a95bc1c0207d
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/44461
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>