Typos and spellings errors fix in config-ref, HA/image guides

Another round of typos/spelling errors fixing, in particular for
config-reference, HA guide and image guide.

Change-Id: Ibc3661e132a0ea4010a5a61f71ef5209ae6655b6
Closes-Bug: #1356970
Merge "Typos and spellings errors fix in config-ref, HA/image guides"