tests: wait for df synchronization before checking test success.

df async behavior caused test failures.

Change-Id: I95a6db93a34e751174bcdda2bbd9b5612acc920b
lustre_tools: protect against llapi_fid2path returning path with final slash.

Noticed a change behavior in llapi_fid2path between Lustre 2.5.0 and Lustre 2.5.2:
llapi_fid2path on root directory FID returns a double final slash:
	> lfs fid2path /mnt/lustre 0x200000007:0x1:0x0
	/mnt/lustre//

This change consists in removing final slash in paths returned by llapi_fid2path(),
to protect robinhood against this.

Change-Id: I76d5589e88d3bc880a7c370985d1f0306c232564
Lustre: fix build for Lustre 2.6 (see LU-3613).

Change-Id: Id1ae8d3991646ddcaf36ba5373884116b587c818
tests: Added missing password file for lustre tests.

Change-Id: I7fcff63213cfa79a638756921935fbd1c790af10
tests: fix backend file name for Lustre/HSM.

Change-Id: I5d37b2dedb213b8dd350595975a7e6e51cb0adf5
release 2.5.3.

Change-Id: Ic0eceec397b3b9d7a9e84db59e07811f6ce1d4dd
tests: make lustre helper script return 0 when llmount is successful.

Change-Id: I0b3541a835cea6c043e127c34f35583dec96b112